Paper 4 Conservation Laws in Physics Drills

Q1 Testing Momentum Conservation

Two trolleys collide and remain joined. Rightward velocity is positive.

quantity	value
mass of trolley A	$(0.500\pm 0.005)\mathrm{kg}$
velocity of A before collision	$(+0.800\pm 0.010)\mathrm{m}{\mathrm{s}}^{-1}$
mass of trolley B	$(0.300\pm 0.005)\mathrm{kg}$
velocity of B before collision	$0$
common velocity after collision	$(+0.495\pm 0.010)\mathrm{m}{\mathrm{s}}^{-1}$

1. Calculate the total momentum before and after the collision. [3]
2. Calculate the percentage difference between the two momentum values. [2]
3. Estimate the percentage uncertainty in each momentum using percentage-uncertainty addition for products. [3]
4. State whether the results support momentum conservation and justify your conclusion using the uncertainties. [2]
5. Calculate the kinetic energy before and after the collision and account for the difference. [3]

Q2 Planning an Energy-Transfer Investigation

A low-voltage electric motor lifts a mass vertically. Plan an investigation to determine how the motor’s efficiency changes with load.

Your plan should state:

1. the independent, dependent and important controlled variables; [3]
2. the measurements needed to determine electrical input energy and gravitational potential-energy gain; [3]
3. a suitable range, repeats and data table structure; [2]
4. how efficiency will be calculated and presented; [2]
5. one specific limitation with a matched improvement, and one safety precaution. [3]