A student investigates the relationship between force and acceleration for a trolley on a runway - Edexcel - GCSE Physics - Question 9 - 2018 - Paper 1

The mass of the moving system can be kept constant by ensuring that the mass of the trolley and the weights used remain unchanged throughout the experiment. The use of the weight hanger can be beneficial for transferring mass to the trolley when needed.

The student could raise one end of the runway slightly to create an angle, allowing the trolley to roll without being attached to the weight hanger. This way, the effects of friction can be minimized, and the gravitational force acting on the trolley would counterbalance the frictional forces, allowing for smoother movement.

In a collision, momentum is conserved as long as no external forces are acting on the system. According to Newton's third law, for every action, there is an equal and opposite reaction, which implies that the forces between the two colliding objects are equal and opposite. Therefore, the total momentum before the collision must equal the total momentum after the collision, which can be expressed mathematically as:

$p_{initial} = p_{final}$

where momentum (p) is given by the product of mass (m) and velocity (v), thus:

$p = mv$.