PAG 1.1 - Comparing Methods of Determining

Question 1

What is meant by freefall?

Answer 1

If the only force acting on it is gravity, no resistive forces are acting or they are negligible

Question 2

What is g?

Answer 2

Gravitational field strength

Question 3

Why can we use SUVAT equations while investigating g

Answer 3

The object will fall with uniform acceleration, force of gravity is constant at the Earth’s surface

Question 4

How can you determine g from a t squared/ h graph?

Answer 4

2/ gradient as it comes from s = ut + 0.5at2

Question 5

How can you determine g from a v2/h graph?

Answer 5

Acceleration will be half the gradient due to
V2 = u2 + 2as

Question 6

Describe how an electromagnet system can be used to determine g?

Answer 6

Magnetic ball can be released by an electromagnet clamped at a known height. The timing system starts when the electromagnet is switched off, and the timer is stopped when the ball lands on the finish pad.

Question 7

What safety precautions should be taken with the clamp in this experiment

Answer 7

Add a counterweight so the stand does not topple over

Question 8

What safety precautions should be taken when using an electromagnet?

Answer 8

Electromagnets heat up over time, and you should switch it off when not in use to minimise the heating effect

Question 9

Suggest how light gates could be positioned to make sure the ball falls directly through them?

Answer 9

Plumb line to demonstrate the predicted path of the object.
This allows the light gate to be positioned in appropriate places so that the ball will fall through them

Question 10

Why should we use a smaller ball over a larger ball in this experiment?

Answer 10

The smaller the effect of air resistance, more accurate results

Question 11

Why should there be a gap between the release position and the first light-gate?

Answer 11

Ensure that the time over which the ball is passing through the light gate is negligible

Question 12

Explain why this experiment would not be valid if the air resistance acting on the ball was not negligible

Answer 12

The ball would not be in free-fall since the acceleration would not be purely due to the force of gravity.
The acceleration would also be variable since air resistance increases with speed, and so the uniform acceleration equations couldn’t be used

Question 13

Suggest why your obtained value for g may not be the same as the accepted value

Answer 13

• resistive forces are acting
• errors in height measurements
• delays in timing equipment

Question 14

What is the advantage of using light gates over a stop-clock in this experiment?

Answer 14

Lower uncertainty in your measurements as stop-clocks involve human reaction times

Question 15

How could your results be improved?

Answer 15

You should take repeat readings at each height and then calculate the mean time taken. You should also ensure that height measurements are taken from the same position each time

Question 16

How should you calculate the uncertainty in your time readings?

Answer 16

The uncertainty in time will be equal to half the range of your time readings.
This can be converted into percentage uncertainty

Question 17

How do you determine the percentage uncertainty in t2?

Answer 17

To calculate the percentage uncertainty of a variable that is squared, you double the percentage uncertainty of t itself

Question 18

What is the minimum repeat readings you should take in this experiment?

Answer 18

You should take at least 3 repeat readings at each height. This allows for anomalous results to be more easily identified

Question 19

What is the equation used to convert an uncertainty into a percentage uncertainty?

Answer 19

Percentage uncertainty=
(Uncertainty/mean value) x 100

Question 20

Would you expect your value of g to be greater or lower than the accepted value?

Answer 20

Lower due to air resistance reducing the downwards resultant force