# Should I study physics?

This quiz is designed to give you some idea of the sort of thing it would be good to know before studying IB physics. You actually do not need to know any physics, I have taught many students who have never done physics before that have ended up with a 7 at higher level. In some ways it is an advantage since everything is new and exciting.

## Maths

Let's check out your existing skills!

\(a = 2\) and \(b = 3\)

\({2(a+b)\over a} =\)

\({2(2+3)\over 2} =5\)

You are going to make a fruit salad and need twice as many apples as bananas. Apples cost 50 cents and bananas cost €1. If you have €10, how many apples can you buy?

From the information provided:

\(0.5a+1b=10\)

\(a=2b\)

\(0.5\times 2b+1b=10\)

\(b= 5\) and \(a=10\)

To check your answer:

\(10 \times 0.5 + 5 \times 1 = 10\)

You are going to make a fruit salad and need twice as many apples as bananas. Apples cost \(a\) cents and bananas cost € \(b\). If you buy \(n\) apples how much will the apples and bananas cost in Euros?

You must convert the price of apples into Euros \(={a\over 100}\)

Cost of \(n\) apples \(= {na\over100}\)

If you buy \(n\) apples then you willl buy \(n\over2 \) bananas so cost of bananas \(= {nb\over2}\)

Total \(= {na\over 100} + {nb\over2}\)

You walk 30 m North then 40 m East.

How far would it be if you walked directly from A to C?

You can use Pythagorus \(\sqrt{(30^2 + 40^2)}=50\)

Alternatively you could estimate that it's about 50 (after all, it's got to be more than 40 and it doesn't look as much as 70).

NB: This is a common 345 triangle!

The graph represents the relationship between the price of apples and the number of apples you buy.

What is the price per apple in cents?

Price per apple is the gradient (or slope) = \(0.2\over1\) = 0.2 Euro = 20 cents per apple.

Alternativelty you could look for the price intercept when the number of apples is 1.

The mass of an apple is measured as it grows and a graph of mass against time is plotted.

The rate of growth in kgh^{-1} is:

Rate of growth = gradient = \(20\over2\)

BUT this would be in g per day so we must convert to kg and hours before the calculation:

\({({20\over1000})\over(2\times24)} ={0.02\over48} = 0.0004\)

The mass of a banana is measured on an electronic balance and found to be 241.32 g

How many significant figures is this?

If this is written in standard form it would be 2.4132 x 10^{2}. This is 5 numbers.

1 sf would be 2 x 10^{2}

2 sf 2.4 x 10^{2}

etc.

Which of the following is the same as 3.14 x 10^{6} cm?

There maybe some confusion over . and ,

I use . as decimal point and, to separate thousands

there are 100 cm per m so the length is \({3.14 \times 10^6 \over 100} = 3.14 \times 10^4\)

The sin of 40° is:

Just put it into you calculator but make sure it's in degrees (D) mode.

## Physics

You actually need to know very little about physics as everything is defined clearly before you start a topic but you will have to have the ability to apply laws to solve problems and understand how models relate to reality.

Electric current is often modeled by water flowing in pipes. The difference in height represents the potential difference and the rate of flow of water the electric current.

What happens to the current flowing through a conductor if the potential difference is increased?

You can see that as the difference in height gets less the rate of flow decreases. If this is analogous to electric current, an increase in potential difference will lead to an increase in current.

Electric current is often modeled by water flowing in pipes. The difference in height represents the potential difference and the rate of flow of water the electric current. If the resistance of the conductor is increased the current is reduced.

To increase the resistance in the water analogy we could:

Reducing the pipe diameter would reduce the flow rate for the same height difference.

The sign of acceleration gives its direction: + is to the right and - is to the left.

An acceleration of -10 ms^{-2} means that:

As stated the sign gives the direction of acceleration and no other information.

The body could be slowing down if it is moving right. If it is moving to the left it will actually be getting faster. Definitions should be applied carefully.

The law of conservation of energy states that energy can not be created or destroyed but only changed from one form to another.

In which of the examples below is energy conserved? Tick all that apply.

If the law says it is always conserved then it always is. Actually (as you will later discover) we should say "energy / mass" but in this example the change in mass is negligible.

Not to mention that you were instructed to select 4 answers!

The relationship between energy and mass is given by the famous equation:

\(E = mc^2\)

- \(m\) is the mass in kg
- \(c\) is the speed of light = 3 x 10
^{8}ms^{-1} - \(E\) is the energy in Joules

Calculate the energy liberated if the mass of an electron (9.1 x 10^{-31} kg) is converted into energy

E = 9.1 x 10^{-31} x (3 x 10^{8})^{2} = 8.19 x 10^{-14} J

Even if you don't understand the concept you can sometimes still answer the question :)

An air rifle pellet is fired at a box full of sand and it comes out of the other side.

From this you could conclude that:

Sand can't turn into air.

We can see that the rifle is an air rifle.

If the pellet disappeared it would break the laws of physics and this very subject could not be studied!

Two rockets pull a large metal bar as shown.

Which of the following shows the motion of the bar?

Sometimes intuition is not enough. If it was, you wouldn't need to study physics.