NSAA Guides

# NSAA Physics: Your Guide to Physics and Advanced Physics in the NSAA

Written by: Matt Amalfitano-Stroud

Physics is one of the three sciences you’ll have to pick from when sitting the NSAA. Depending on your confidence with the subject, you can take on questions centred on physics and advanced physics, but what topics will these questions cover? Today, we’re going to look at the NSAA specification to see what you need to revise for Parts B and X of the NSAA, aka, the physics sections.    1/4

## BASICS OF THE NSAA

This should hopefully be obvious to you by now, but we’ll quickly revise our knowledge of the NSAA to confirm everything we know so far. ### What is the NSAA?

Most courses at the University of Cambridge require you to complete an admissions test, and the Natural Sciences Admissions Assessment (NSAA) is the test you’ll need to complete for

The NSAA is a two-section, multiple-choice examination that covers the three core sciences, Physics, Chemistry and Biology, alongside Mathematics. Throughout the two sections, you will need to complete three lots of 20 questions (60 questions in total), within the time limit of 60 minutes per section, giving you two hours. This chart explains how the exam is laid out:

#### NSAA Format Chart

Within Section 1 of the paper, there will be 4 parts of 20 questions available, Parts A-D. Part A is the Mathematics part, while B-D house questions for the three sciencesYou will only answer 2 parts here, Part A and any one of the sciences. Section 2 is similar but without the Mathematics part. The parts available are labelled X-Z.

### How is the NSAA Scored?

Like many other Cambridge admissions tests, the NSAA is scored on a scale of 1.0 – 9.0. Each part is ranked separately on this scale, with the three scores then being combined into your final score. but it’s important to understand the basics when preparing.

The conversions between raw marks and final scores are different between each part. Take a look at the conversions in the charts below:

#### NSAA Section 2 Score Conversion 2021

You don’t necessarily pass or fail the NSAA, there isn’t a benchmark score that you need to hit to guarantee a spot at interviews. The admissions team will use your grade alongside your personal statement to make a judgement on whether you could be a good fit for the course.

If you want to take a deeper dive into the NSAA as a whole, you can find everything you need to know in our

Build your NSAA skills with Exams.Ninja!

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## PHYSICS IN NSAA PART B

In Section 1, Part B of the NSAA, you’ll be taking on standard-level physics questions based on a variety of topics that you should have covered during your education. Let’s take a look at everything you’re going to need to study for! Part B of the NSAA is the first of three options you can pick in Section 1 of the NSAA (after you’ve completed Part A of course). There will be 20 questions to answer based on all of the topics that you will find in the NSAA Specification. There are seven major topics to cover, so let’s take a brief look at them right now!

Before we get started, let’s remind ourselves of the essential SI prefixes, or Scientific Quantities and Units:

nano- 10–9

micro- 10–6

milli- 10–3

centi- 10–2

deci- 10–1

kilo- 103

mega- 106

giga- 109

### Electricity

This is a topic you’ll likely have been studying since primary school! Our understanding of electricity has developed so much in such a short period of time (relative to other sciences), so it’s only natural that there will be a lot of revision to do!

At this level, the key thing to understand is electrical circuits. Here are some of the things you’ll need to keep in mind before entering the exam:

You’ll need to understand the basic layout of a circuit diagram, such as the ones you’ll see below. This also extends to the different symbols to represent components of a circuit, such as cells, resistors, switches and more.

Make sure you can definitely tell the difference between series and parallel circuits, as pictured below. The difference essentially comes down to if a circuit has more than one loop within.

There are several definitions to remember, including:

• Circuit – A flow of electricity
• Current – A stream of charged particles travelling through a conductor.
• Resistor – A component to generates electrical resistance within a circuit.
• Voltage – The measure of difference of electrical energy between two parts of a circuit

There are also various other concepts that you’ll need to know, including direct currents, alternating currents, insulating materials and conductive materials.

There are also plenty of equations to memorise! Here are the key ones you’ll need for Part B, where Q = Charge, I = Current, V = Voltage, R = Resistance, P = Power and t = Time and E = Energy

I = Q/t

V = E/Q

Resistance: (V = IR) and (R = V/I)

P = E/t OR P = IV = I2R = V2/R

E = ItV

Also featured within the NSAA Specification is Electrostatics, or, Static Electricity. There’s not to much you’ll need to go through, just ensure that you understand how it relates to insulators and how its charges work, as well as the dangers surrounding it.

### Magnetism

This one’s another primary school staple, although the NSAA goes far beyond putting N and S against each other to watch them attract!

It’s always best to start with the basics, such as the properties of standard magnets, including their poles and fields. You can get an idea of how a typical bar magnet’s fields look at different stages of attraction.

Diving into the more complex topics, you’ll need to revise the following:

#### Induced Magnetism

This is the process of giving magnetic properties to non-magnetic metals, such as steel alloys. It’s done by reorienting the particles of the material to line up the north and south ends of each within a magnetic field.

#### Electromagnetics

When you want to create a controllable magnetic field, then you’ll need to use electromagnetics. You’ll need to understand how this is achieved and factors that determine a magnet’s strength. Electromagnetic Induction is also covered in the specification, so you’ll need to brush up on how this works.

#### The Motor Effect

This essentially means that a wire carrying currents will produce a magnetic field. If the field interacts with another, a force will be created that pushes the wire towards a right angle. An equation you should memorise for this is F = BIL, where F = Force,  B = Flux Density, I = Current and L = Length of Wire. Also, you will need to know how this relates to DC Motors.

#### Transformers

A transformer is a device that changes voltage and current, whilst keeping power the same. Thankfully, one equation will see you through the majority of questions regarding transformers.

N¹/N² = V¹/V²

N¹ is the number of turns on the primary coil and N² is the number of turns on the secondary coil, with the V values being their respective voltages.

### Exams.Ninja Tip

One small piece of information that you will want to remember is that transformers only work with one kind of current, Alternating Currents (AC). They will not work with Direct Currents (DC). While unlikely, there’s always a chance that a question will try to catch you out with this information.

### Mechanics

This is what comes to many people’s minds when they hear “Physics”. This topic is all about forces, energy, movement and the many ways of measuring and using them.

Scalars – Quantities with a magnitude but no directions (e.g. time, speed, distance)

Vectors – Quantities with both a magnitude and direction (e.g. displacement, acceleration, velocity)

You’ll need to know how to apply the following equations to questions within the NSAA:

Speed = Distance/Time

Velocity = Change in Displacement/Time

Acceleration = Change in Velocity/Time

Average Speed = Total Distance/Total Time

v² – u² = 2as

That last one is known as the Equation of Motion, where u = initial velocity, v = final velocity, a = acceleration and s = displacement. You’re also going to need to understand how these equations are presented graphically, such as the example below of a Velocity Time Graph:

#### Forces and Extensions

Forces and Extensions is another major part of this topic. A force is, of course, defined as a push or pull on an object that causes a change in its velocity. Essentially, forces are responsible for changing the motion of objects with mass.

There are a bunch of different types of forces you’ll need to remember:

Weight – A force that acts due to gravity.

Normal Contact – The force of a stationary object exerted against a surface.

Drag – An aerodynamic force that opposes objects within the air.

Friction – A resistive force caused by two objects sliding against one another.

Magnetic – The forces generated by magnetic fields.

Thrust – A force acting perpendicular to a surface.

Lift – A force of raising or lowering.

Tension – A pulling force caused via a string or similar object.

With forces, you’ll also need to understand their extension. This is an object increasing in length, as opposed to compression, and goes hand in hand with the concept of elasticity (although inelastic extension is also possible once an object has reached its elastic limit, also known as inelastic deformation).

Here’s an example of a Force-Extension Graph:

Here’s a reminder of some of the Laws you will need to remember during your revision at this level:

#### Hooke's Law

Hooke’s law says that force is proportional to extension, based upon the idea of ‘String Constant’ which is the constant of proportionality. the relationship is summarised in this equation.

F = kx

F = Force applied to material/string (N)

x = Extension of material/spring (m)

k = Spring constant (Nm -1)

#### Newton's Laws

1. A body will remain at rest or in a state of uniform motion in a straight line unless acted on by a resultant external force.
2. Force applied is directly proportional to the rate of change of momentum in an object.
3. If body A exerts a force on body B, then body B exerts an equal and opposite force of the same type on body A. This is “Reaction Force”.

Let’s take a quick look at the definitions of mass and weight:

Mass – A measure of how much matter an object is made up of.

Weight – the force of gravity on an object.

Gravity is defined as the force that attracts objects towards the earth. We can easily express weight as w = mg.

A Resultant Force is required for an object to accelerate. It is defined as the difference in forces when a system of forces is acting on an object.

Momentum (p) is simply defined as mass in motion. It can be expressed as:

p = mv

You’ll need to be sure you revise the concepts of conservation of momentum and changes in momentum.

Lastly, for Mechanics, you need a good understanding of energy for the NSAA. Energy relates to everything we’ve spoken about so far as any form of force or movement requires and generates energy. Here are a few formulae that you’re going to need to know:

Work as Energy (E): E = Fd

Power (P): P = E/t

Kinetic Energy (KE): KE = 1/2mv²

Remember that energy cannot be created or destroyed, so we use the concept of energy transference to determine things such as potential energy and energy efficiency. You can use this equation when working out energy efficiency:

Efficiency = Useful Energy Out/Total Energy In x 100

However, bear in mind that there is no such thing as a 100% efficient energy transfer.

### Thermal Physics

As the name implies, this sector of physics is all about heat. The basic rule of this topic that you need to know is that heat will always move from a hot area to a colder area. The bigger the difference is in temperatures, the quicker the transfer will be. Let’s look at the three methods of transfer:

#### Conduction

Conduction is the transfer of heat or energy particles to a neighbouring object via vibrations. This needs to occur between two conductors typically, as an insulator will have the opposite effect on any energy or heat present.

#### Convection

This is the process of heating up higher energy particles in cooler areas and usually occurs within liquids and gas. These particles are transferred in what is called “Convection Currents”.

#### Electromagnetics

When you want to create a controllable magnetic field, then you’ll need to use electromagnetics. You’ll need to understand how this is achieved and factors that determine a magnet’s strength. Electromagnetic Induction is also covered in the specification, so you’ll need to brush up on how this works.

In relation to Thermal Physics, radiation is a method of heat transfer that is caused by the emission of infra-red electromagnetic waves. One rule to consider here is that all objects emit and absorb radiation.

Now let’s take a look at Heat Capacity, otherwise known as Thermal Capacity. Heat Capacity is defined as the number of heat units required to raise the temperature of an object by one degree. Heat Capacity is measured in joule per kelvin and can be calculated using the following equation:

Specific Heat Capacity = thermal energy/(mass x temperature)

### Matter

Matter is all about the structure of all objects in the universe determined by their atoms. As you should know at this stage, there are three stages of matter:

Solid: A body whose atoms are stuck in a rigid and consistent structure.

Liquid: A body whose atoms are free and have weaker forces of attraction to one another.

Gas: A body whose atoms are spaced out and completely unstructured.

All elements can transition between the three states, it’s simply about rearranging the atoms. Some objects are easier to change than others and will typically be caused by changes in temperature (e.g. melting a solid into a liquid via raised temperature, evaporating a liquid into a gas).

#### Ideal Gases

The Kinetic Theory of Gases is a simple model used to describe the behaviour of gases through the motion of tiny particles or atoms. This model can be used to describe an “Ideal Gas”, which is a hypothetical gas which has no form of interaction and occupies no space, essentially meaning it perfectly follows the laws of gas.

The equation for Ideal Gases is as follows:

PV = nRT

Here, P = Pressure in Pascals, V = Volume (m3), n = Number of Moles Gases, R = Ideal Gas Constant, T = Absolute Temperature

Lastly, let’s take a look at Density and Pressure.

Density is defined as the measure of how compact a substance is and is expressed via Density = Mass/Volume.

Pressure is expressed as P = F/A, meaning it is equal to the normal force divided by area.

### Waves

Waves in physics are defined as propagating, dynamic disturbances of one of more quantities, sometimes taking place in a periodic fashion. These can cover a lot of different topics in reality, as waves are measured in many fields of science. Here’s a very simple diagram of a wave with all of its features labelled.

The key things to understand here are:

Amplitude – The height of the wave from its resting position to its peak.

Wavelength – The physical length of the wave, measured between two similar points at adjacent waves (e.g. peak to peak).

Frequency – This is defined as the number of complete waves per second and is measured in Hertz (Hz).

These are the key equations you will need for the NSAA:

Frequency = 1/Period

Wave Speed = frequency x wavelength OR Wave Speed = Distance/Time

We can characterise waves by their type, either Transverse or Longitudinal:

Transverse – Waves that travel in a direction perpendicular to the direction of oscillation.

Longitudinal – Waves whose particles oscillate parallel to the direction of the travel.

There are various wave behaviours you are going to need to understand, which you’ll find below:

#### Reflection

Where a wave bounces off a surface. The angle that the wave hits is known as the angle of incidence, which will cause it to reflect at the angle of reflection.

#### Refraction

This usually relates to light, but in waves, it relates to the angles and direction a wave will travel when it enters a different medium.

#### Diffraction

This relates to how waves can bend around corners in certain conditions. It is most likely to occur when a wavelength is similar to the size of the gap it’s passing through.

Some other important topics to cover include drawing ray diagrams in relation to optics, understanding the properties of sound waves (and their variations) and understanding the properties and uses of electromagnetic waves.

This is the last topic you’re going to need to prepare for in the Standard Physics of the NSAA. Let’s take a look at some of the key areas you’ll need to revise:

#### Atomic Structure

This is an area that has been highly debated throughout history, with a variety of models being produced over the years. There are a variety of things you’ll need to consider here, including Subatomic Particles (particles that make up atoms), and the Nuclear Model, specifically the Bohr model. The key take away from this model (which you’ll find below) is that protons and neutrons can be found in a dense, positively charged nucleus, while electrons are found in orbitals or energy levels around the nucleus.

Ionisation – The process in which an electron is given enough energy to break away from an atom, with the end result of two charged ions or particles.

There are three forms of radiation. Let’s take a look at each one:

##### Alpha Particles

Alpha Particles are Helium nuclei (2 protons and 2 neutrons), which have the smallest range of the three radiation types but are the most ionising form of radiation. They can however be blocked by practically any surface.

##### Beta Particles

These are high-speed electrons with a mass of 0 and a charge of -1. They have a medium-range, medium ionising power and are harder to block, with aluminium being the most effective material.

##### Gamma Rays

Gamma Rays are photons with a mass and charge of 0. They have the longest range but are the least ionising and can be blocked by materials with a high atomic number, such as lead.

Be sure to remeber the different properties of each radiation type, as they will ocme into play within the NSAA questions.

Let’s take a look at the equations of decay each form of decay:

Alpha DecaynzX =n – 4 z – 2 Y +4 2 α

Beta DecaynzX = n z + 1 Y + 0 -1 β

Gamma Decay – There isn’t really an equation for this, as the nucleus just changes from a high energy state to a low energy state, releasing the gamma photo in the process.

##### Half-Life

Half-Life is defined as the average time it takes for the number of nuclei in a radioactive sample to halve. Questions in the NSAA about this will likely ask you to work out the half-life of a radioactive sample. These should be presented in the form of an exponential decay graph.

In this example, a good place to start is at Time = 0. We can see that the counts per minute (a measure of radioactivity) is 80, so all we have to do is see how long it takes for that number to halve to find the half-life. We’re looking at the amount of time it takes for the curve to fall to 40 counts per minute, and the answer is 2 days. So the half-life is 2 days.

Be wary of the concept of Background Radiation while answering questions like this. Background Radiation is defined as the remaining uniform microwave radiation left behind from the creation of the universe.

That covers all the general concepts you can expect to find within Part B of the NSAA. However, that’s only half the story for NSAA Physics, as we now need to look at the Advanced Physics that you’ll find in NSAA Part X.

If you want to learn more about Section 1 as a whole and get some helpful revision tips, you should check out our guide to Section 1 of the NSAA.

Want to learn even more about NSAA Physics?

The NSAA Preparation Platform contains over 100 expertly written tutorials that teach you everything you need to know about NSAA mathematics and science, as well as plenty of super revision and exam tips!

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## ADVANCED PHYSICS IN NSAA PART X

Now we’ve got the basics out of the way, it’s time to take a deeper dive into these topics and look at some news ones so you can get ready to prepare for Part X of the NSAA! Just like Section 1, Section 2 will see you choosing one of three parts to answer 20 questions for. Since you’re reading this guide, you may well be thinking about choosing Part X, Advanced Physics.

One thing to bear in mind with Part X is that the Physics aren’t really “advanced” in the sense of tackling difficult topics. It’s more about how the questions are asked, as some of them can try to catch you out with unfamiliar scenarios or techniques.

Everything you’ve learnt about Standard Physics will be needed here, as it forms the foundation for everything covered in Part X. Let’s jump straight into it and find out what you need to know!

### Forces and Equilibrium

This time, things start with Forces and Equilibrium. We discussed Vectors before, so let’s take a look at some additional concepts and “Methods” surrounding them:

#### Vector Notation

This relates to the variety of ways that vectors can be written and displayed. For example, they could be underlined lower case letters (a) or upper case letters with arrows on top. You can even make letter chains like “AB”. For the NSAA, the important thing is that you can recognise them within the question.

### Exams.Ninja Tip

When doing practice questions, be sure to seek out examples of each of these kinds of notation so you can see how they’re used in the context of an actual problem

#### Resolving and Combining Vectors

These are two question types that you’re very likely to see in the NSAA. Either of these can be done via drawing or calculation (calculation is the more popular method of the two). This is definitely more mathematical than a lot of other topics in the NSAA, but its an important one so you need to get to grips with it!

#### Moments

When working with physics at this level, we tend to stay within linear mechanics, which essentially means we’re working within two dimensions. However, we use moments to measure rotational force, which is pretty much always more complicated than dealing with just two plains of movement. Moments can be expressed as so:

Moments = Force x (perpendicular) Distance (between pivot to the line of action of the force)

Thankfully, this isn’t something likely to come up in the NSAA but it’s something you’ll need to get to grips with going forwards.

#### Contact Forces

Contact Forces are the perpendicular forces that are present whenever two objects are in contact. There are two kinds of contact forces:

##### Normal Contact Forces

We briefly touched on this earlier, but a Normal Contact Force is the force that acts upon two stationary objects. If a block is sitting on a table, then there will be an upwards normal contact force pushing the block upwards to counteract the downwards force caused by the earth’s gravitational pull.

##### Frictional Contact Forces

This is the force that is present between two objects that are moving while in contact. This force prevents the objects from sliding away indefinitely, so it’s definitely important! Two terms you will need to know for this topic are “Smooth”, meaning a frictionless surface and “Rough”, meaning a surface with friction. In the NSAA, it will be assumed in most questions that any surfaces involved in questions will be smooth, so frictional contact forces won’t come into play.

#### Centre of Mass

The Centre of Mass, or Centre of Gravity, of an object, is the point at which the full mass of the body will be acting. Any object will have a centre of mass and it is especially useful to find this out for an object that is not a simple cube or sphere. This is because having one fixed point is much easier than trying to calculate a body’s entire mass.

You can find the Centre of Mass in various ways, be it by locating the pivot point, splitting complex shapes into regular ones or simply finding the middle of the shape (which only works for simple shapes).

### Kinematics

We covered most of what you need to know about Kinematics already thankfully! However, you need to know and be able to solve SUVAT Equations, or the Equations of Motion. For these, we must understand that s = Displacement, u = Initial Velocity, v = Final Velocity, a = Acceleration and t = Time.

v = u + at

s = ut + 1/2(at)2

s =  ((u + v)/2)t

v2 = u2 + 2as

Remember the following points:

SUVAT equations only work in one-dimension.

Define which direction is positive before beginning the equation.

Use values from the question as much as possible when needing to do multiple equations.

### Newton's Laws

We outlined Newton’s three laws earlier on, but there is one other piece of information relating to it that you’ll need to keep in mind, as it will likely come up in the NSAA.

“Drag force increases speed, which is known as terminal velocity. This relates to both air resistance and liquids.”

### Exams.Ninja Tip

One type of question you may come across is explanation questions. These will typically ask you to review another person’s explanation of a scenario or concept and identify an error in their thinking.

To prepare for these, it’s recommended that you practice writing explanations yourself, even though you won’t be required to do so in the exam. Doing this will not only help you cement the knowledge in your mind but will also help you when making judgements about other people’s work. One way to practice doing this is to write your explanations as a step-by-step method, like a recipe or instruction list.

Another type of question that may come up in the NSAA is connected body questions. These will most likely be simple F = ma questions with multiple bodies, so the key to answering these is to answer methodically and go one step at a time.

### Momentum

Momentum is covered extensively in other topics, but there are a couple of bits you’ll need to know for Advanced Physics. Firstly, as a couple of basic pieces of knowledge:

You must know how momentum is defined (mass x velocity).

You must know how conservation of momentum works in 1-Dimensional situations.

You must know how to apply force = rate of change of momentum.

Beyond this, you should also be aware of elastic and inelastic collisions. An elastic collision is defined as a collision with no loss of kinetic energy, while inelastic collisions will change kinetic energy into another form.

Coalescence – Since most collisions do not have a perfect ‘bounce-back’ response, there will usually be some form of sticking between two bodies. This is known as Coalescence.

One last equation to be aware of is the equation for Impulse of Force:

Impulse = F∆t

### Waves

Coming back to Waves, let’s take a quick look at a few more concepts:

#### Superposition

This is the term used for two waves combining after pushing against each other at equal strength. This can take place as either ‘Constructive Interference’, as the combined wave will be bigger, or ‘Destructive Interference’, because the resulting wave is smaller. These resultant waves will sometimes be called Stationary (or standing) Waves.

A common example of this is a rope with each end creating nearly identical waves that meet and create stationary waves.

#### Nodes

Part of the NSAA specification states that you will need to be able to identify Nodes and Antinodes.

These are essentially the points of no displacement (nodes) and maximum displacement (antinodes) within a stationary wave formation.

The distance between adjacent nodes or antinodes will always be equal to half of a wavelength.

### Electricity

Finally, let’s check out a few more things you’ll need to revise for electricity questions in the NSAA:

#### Ohm's Law

Ohm’s Law states that voltage across a conductor will be directly proportional to it’s current whenever conditions remain constant. You will need to know how to apply this for certain questions within the NSAA.

#### Kirchhoff's Laws

These laws state the following:

1. Current is conserved into and out of junctions
2. In any loop, the voltage gain must be lost

These laws will specifically be required for certain circuit problems in the exam.

One last equation to be aware of is the equation for Impulse of Force:

Charge = current x time

Potential Difference = work done/charge

Resistivity = resistance x cross-sectional area/length

So, that concludes the required knowledge for physics in the NSAA. It’s a lot to get through, but you’re going to have to spend time revising every topic thoroughly in order to give yourself the best chance of a great score.

If you want to learn more about Section 2 as a whole, you can check out our. Alternatively, if you’re looking for even more NSAA revision material, you can check out, which contains over 100 in-depth tutorials, along with tonnes of practice questions and past papers!

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## NSAA PHYSICS PRACTICE QUESTIONS

With all knowledge now in mind, let’s try some NSAA practice questions to get a proper idea of how you will need to use this knowledge in the actual exam. ### NSAA Physics Question 1

An elevator has a mass of 1,600 kg and is carrying passengers that have a combined mass of 200 kg. A constant frictional force of 4,000 N retards its motion upward. What force must the motor provide for the elevator to move with an upward acceleration of 1 ms-2?

Assume: g = 10 ms-2

A) 1,190 N

B) 11,900 N

C) 18,000 N

D) 22,000 N

E) 23,800 N

Weight of elevator + people = mg = 10 x (1600 + 200) = 18,000 N

Applying Newton’s second law of motion on the car gives:

Thus, the resultant force is given by:

FM = Motor Force – [Frictional Force + Weight]

FM = M – 4,000 – 18,000

Use Newton’s second law to give: FM = M – 22,000 N = ma

Thus, M – 22,000 N = 1,800a

Since the lift must accelerate at 1ms-2: M = 1,800 kg x 1 ms-2 + 22,000 N

M = 23,800 N

### NSAA Physics Question 2

A 20 A current passes through a circuit with resistance of 10 Ω. The circuit is connected to a transformer that contains a primary coil with 5 turns and a secondary coil with 10 turns. Calculate the potential difference exiting the transformer.

A) 100 V

B) 200 V

C) 400 V

D) 500 V

E) 2,000 V

F) 4,000 V

G) 5,000 V

Using Ohm’s Law: The potential difference entering the transformer (V1) = 10 x 20 = 200 V.

Now use N1/N2 = V1/V2 to give 5/10 = 20/V2.

Thus, V= 2,000/5 = 400 V

### NSAA Physics Question 3

The half-life of Carbon-14 is 5,730 years. A bone is found that contains 6.25% of the amount of C14 that would be found in a modern one. How old is the bone?

A) 11,460 years

B) 17,190 years

C) 22,920 years

D) 28,650 years

E) 34,380 years

F) 40,110 years

The percentage of C14 in the bone halves every 5,730 years. Since it has decreased from 100% to 6.25%, it has undergone 4 half-lives. Thus, the bone is 4 x 5,730 years old = 22,920 years

### NSAA Physics Question 4

Which of the following statements are correct?

1. Electromagnetic induction occurs when a wire moves relative to a magnet.
2. Electromagnetic induction occurs when a magnetic field changes.
3. An electrical current is generated when a coil rotates in a magnetic field.

A) Only 1

B) Only 2

C) Only 3

D) 1 and 2

E) 2 and 3

F) 1 and 3

G) 1, 2 and 3

Electromagnetic induction is defined by statements 1 and 2. An electrical current is generated when a coil moves in a magnetic field.

### NSAA Advanced Physics Question 1

A uniform rod of length 1 m is balanced on 3 supports so that it is in equilibrium. The position of the first support is at x1 = 0.1 m, where x is the distance along the rod. The second support is at x2 = 0.6 m and applies a force, F2, of 4 N to the rod. The third support is at x3 = 0.8 m and applies a force, F3, of 6 N to the rod.

What is the force applied by the first support, F1?

A) 4.5 N

B) 5.0 N

C) 5.3 N

D) 5.5 N

E) 6.7 N

F) 7.3 N

G) 10.5 N

H) 11.0 N

The mass of the rod is unknown so take moments about the centre of mass at xc = 0.5 m.

F1 (xcx1) = F2 (x2 – xc) + F3 (x3 – xc)

F1 (0.5 – 0.1) = 4 (0.6 – 0.5) + 6 (0.8 – 0.5)

0.4F1 = 0.4 + 1.8 = 2.2

∴  F1 = 22/4 = 5.5 N

### NSAA Advanced Physics Question 2

A spring is used to lift 20 cm3 of loosely packed sand in a small bucket. The spring constant, k, is 4 Nm-1 and the sand causes the spring to extend by 10 cm. What is the density of the sand at this packing fraction? (Take g = 10 Nkg-1).

A) 3,200 kgm-3

B) 32,000 kgm-3

C) 1,000 kgm-3

D) 2,000 kgm-3

E) 20,000 kgm-3

F) 2,500 kgm-3

G) 4,500 kgm-3

H) 800 kgm-3

Work out mass of sand by using Hooke’s law for a spring to obtain the weight. Then find density.

Weight = Force on spring

mgkx

m = kx/g = (4 x 0.1)/10 = 0.004 kg

V = 20cm³ = 20 x 10-6m³

Density, ρ m/= 0.04/(20 x 10-6 2000kgm-3

### NSAA Advanced Physics Question 3

A wave approaches the boundary between two mediums at an angle of 30° to the normal. Upon entering the second medium it is refracted such that it now travels at 45° to the normal. The wave travels at 5 ms-1 in the first medium.

What velocity does the wave travel at in the second medium?

A) 8/√3 ms-1

B) 8√3 ms-1

C) 8/√2 ms-1

D) 10√3 ms-1

E) 5/2 ms-1

F) 10√2 ms-1

G) 5/√2 ms-1

H) 5√2 ms-1

n = v1/v2 = sinθ1/sinθ2

n = sin30/sin45

Remember: sin30 = 1/2, sin45 = 1/√2

∴ n = 1/2 ÷ 1/√2 = √2/2

v2 = v1/= 5 ÷ √2/2 = 10/√2

v2 = 5√2 ms-1

### NSAA Advanced Physics Question 4

A hydroelectric dam stores energy by pumping water from a lower reservoir to a higher reservoir using an electric pump (supplied with 100V and  10A). This power can then be harnessed again by allowing the water to fall down to the lower reservoir, driving a turbine, generating electricity. It takes 100S for the pump to lift 1000kg of water to a height of 75m above the reservoir. This mass of water is then used to drive a turbine, which converts the gravitational potential energy of the water into electrical energy with a 33.3% efficiency. What percentage of energy is lost in the act of storing energy using this hydroelectric dam?

A) 0%

B) 25%

C) 33.3%

D) 50%

E) 66.7%

F) 75%

G) 80%

This question is very wordy, but the crucial step is noticing that the electrical energy into the pump (given by the equation E = Vlt) is 1MJ but the gravitational potential energy of the water (given by the equation E = mgh) is 0.75MJ. You therefore multiply the efficiencies of the two processes for an overall efficiency of 75% x 33.3% = 25%, so 75% of the energy is lost.

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