A student investigates the relationship between force and acceleration for a trolley on a runway - Edexcel - GCSE Physics Combined Science - Question 6 - 2018 - Paper 1

To keep the mass of the moving system constant, the student can transfer a specific amount of mass between the trolley and the weight hanger. For instance, if a certain mass is removed from the trolley, an equal mass should be added to the weight hanger, ensuring that the overall mass of the system remains unchanged.

To improve the procedure and compensate for frictional forces, the student could raise one end of the runway so that the trolley rolls along a slope. This alteration allows the gravitational force on the trolley to counterbalance the frictional forces, enabling the trolley to accelerate more efficiently without being hindered by friction. Furthermore, the student may consider using smoother surfaces for the runway or applying lubrication to reduce friction.

Momentum is conserved in the collision between objects Q and R due to Newton's third law, which states that for every action, there is an equal and opposite reaction. Therefore, the force exerted by object Q on R during the collision is equal and opposite to the force exerted by object R on Q. As a result, the total momentum before the collision, which can be represented as the sum of the momentum of both objects, remains constant after the collision, as any change in momentum of one object results in an equal and opposite change in the momentum of the other. This can be mathematically expressed as:

$ext{Change in momentum of Q} = - ext{Change in momentum of R}$

This equation confirms that the overall momentum in the system is conserved.