Paper 4 Dynamics Drills

Q1 Force and acceleration of a trolley

A student pulls a trolley of known mass using a force sensor. The acceleration is measured using a motion sensor.

Pulling force $F/\mathrm{N}$	0.40	0.70	1.00	1.30	1.60
Acceleration $a/\mathrm{m}{\mathrm{s}}^{-2}$	0.18	0.43	0.68	0.94	1.18

The expected relationship is

$$F=ma+F_0,$$

where $F_0$ is an approximately constant resistive force.

1. Plot $F$ against $a$ on the grid below and draw a straight line of best fit. [5]

2. Explain how the trolley mass and resistive force can be obtained from the graph. [3]
3. Use your graph to determine the trolley mass and $F_0$. [4]
4. Suggest one physical reason why $F_0$ is non-zero. [1]
5. State one practical precaution when using the force sensor. [1]

Q2 Momentum investigation

Two low-friction trolleys collide on a track. A student measures their velocities before and after collision using light gates.

1. State two measurements needed to test conservation of momentum. [2]
2. Explain why the track should be level. [2]
3. Describe how repeated trials improve confidence in the conclusion. [2]
4. State one observation that would suggest significant external impulse during the collision. [1]