## Questions like the HSC 2018 exam

Due to copyright the actual exam questions can not be published here.

Please refer to the 2020 HSC Physics exam for the published questions.

## like question 9

A proton is ejected from an exploding star in a galaxy 10 million light years away. On arriving at Earth it is detected as travelling at 0.9999999c.

Which of the following statements is true?

1. The proton experience less distance than 10 million light years
2. The mass of the proton was detected as larger.
3. The proton experienced a little less than 10 million years during the journey.
4. It is impossible for the proton to travel at 0.9999999c.
Useful Reference:

The interactive animation shows that a cylinder contracts in length when the cylinder is moving and the clock is stations. Imagine the cylinder has the length equal to the distance to the distant star. From the clocks reference frame the cylinder contracts when in motion, or the distance to the distant star contracts.

## like question 16

You observer a spacecraft is too long to fit inside a box when stationary relative to you.

The spacecraft now travels at 0.5c relative to you, and you observer that the spacecraft is the same length of the box. When the spacecraft in just inside the box the second hands of clocks at A and B are pointing up.

Which of the following statements is true for a passenger on the spacecraft.

1. The box contracts so the spacecraft does not fit, and clock B is ahead of clock A.
2. The box contracts so the spacecraft does not fit, and clock A is ahead of clock B.
3. The box expands due to length contraction of the spacecraft, allowing it to fit in the box, and clock A is ahead of clock B.
4. The box expands due to length contraction of the spacecraft, allowing it to fit in the box, and clock B is ahead of clock A.
Useful Reference:

In the animation the spacecraft is stationary the clocks are synchronised because the photons arrive at the clocks synchronised. When in motion the events are not synchronised. The photon arrives at the back of the spacecraft before the front. The spacecraft must contract to maintain the event at the middle mirror.

In the thought experiment in the question, if the occupant in the train is facing the same direction as the observer on the ground, then the mountain appears to be moving from right to left. There are two ways of coming up with the correct answer.

• With the mountain in motion from right to left the back of the mountain is the right side. In time the back is ahead of the time in the front. The event to the right, photo 2, will happen before photo 1.
• Because the mountain is moving it is length contracted. The right side of the mountain, Y, will pass the right side of the train before the left side of the mountain, X, has an opportunity to reach the right side of the train. So the event to the right, photo 2, will happen before photo 1

When the spacecraft is stationary the photons that fly towards the back and front hit the ends of the grid synchronised. With the grid in motion the back photon hits first. the back is now ahead in time compared to the front.

## question 34 b ii

### 6 mark

The following is a nuclear reaction that produces a Neon nucleus and a gamma ray

4
2
α +
16
8
O →
20
10
Ne +
γ

The table shows the masses of the particles in the reaction

ParticleMass (u)
4
2
α
4.002603
16
8
O
15.994915
20
10
Ne
19.99244
γ
0

Assuming the What is the energy of the gamma ray?