AQA Physics Unit 2 - Unofficial Markscheme

I thought they said they increased the upwards force to 1850 N rather than added 1850 N of upwards force.

MISPLACED QUESTIONS + ANSWERS

There was a question with two graphs where you had the choice of greater than / less than / equal to ?
There was another question where it asked what the distance/time graph showed about the speed?


CREDIT:

What are the materials inside a plug? [4]
Pins are brass because they conduct electricityCasing is plastic because it is an insulator

For pins could you just of put metal?

that's exactly what I did! Are you doing a level physics then? I can't wait, it seems so fun, even if i do sound a bit sad for saying that.

The answer for the first question was worth two marks and the answer was greater than because the ball is moving at a higher acceleration so a higher drag is needed to get it to achieve terminal velocity

Surely if it is the same ball bearing then there will be the same weight pulling downwards and therefore the same drag force would be needed to achieve terminal velocity? However, I thought the question was actually whether there was more drag force at a certain time (can't remember what time it was) rather than how much drag force was required to reach terminal velocity. The one in hot oil was still accelerating whereas the one in cold oil had reached terminal velocity. Therefore, there must have been less drag force in the hot oil so the answer was less than.

I thought that a larger speed meant more resistance was needed to balance it to equal terminal velocity?

All that is required to reach terminal velocity is for the drag force to be equal and opposite to the force of gravity pulling down so that there is 0 resultant force and therefore 0 acceleration. I'm not sure what you mean by a larger force being needed for a larger speed. It is true that as things accelerate the resistance increases but that won't change the terminal velocity.

But the question showed us too graphs of two identical objects travelling at different speeds and asked us which had the greatest drag, i might be wrong, so i appreciate you trying to explain. The one that is travelling at a faster speed of 100m/s needs 100 (idk the units) of drag, whereas an object at travelling at 50m/s needs 50 units of drag to achieve a resultant force. So the object travelling at a higher speed has more units of drag acting on it.

Although the objects were the same, the medium they were falling in wasn't. One was falling in hot oil and the other was falling in cold oil. I will try to explain it in another way. The speed they were falling at wasn't really relevant. What matters is their acceleration. The distance-time graph for the one in hot oil was curving upwards (meaning the ball was accelerating) whereas the one for the cold oil was a straight diagonal line (meaning the ball had already reached terminal velocity). If we look at the ball in cold oil, the resultant force acting on it must have been 0 N because it had reached terminal velocity (i.e. there was no acceleration) and F=ma (so 0 resultant force means 0 accleration since the ball must have had a non-zero mass). If we say that weight of the ball was, for example, 1 N, the drag force must also have been 1 N upwards in order to balance this and give 0 resultant force. However, in the hot oil, the ball was still accelerating downwards. Therefore, the weight must have been larger than the drag force as there must have been a net resultant force to cause the acceleration. Since the ball was the same and so had the same weight of 1 N, the drag force must have been less than 1 N. Therefore, the drag force in the hot oil must have been less than the drag force in the cold oil. Sorry that was a bit long, I just wanted to try to give a better explanation.

IT WAS DURING not before mate for question 1

I got 47/60. What grade?

Which question?

84kg
22m/s2
0.015A

she's talking about the circle question. It was defiantly not 'as' it's either before or after

Wasn't it 12 m/s^2

because they increased the upwards force to 1850 and to find the resultant force you minus the downward force (weight) which was 840 giving you 1010.
1010N / 84kg = 12.02 = 12 m/s^2?