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

To keep the mass of the moving system constant, the student should ensure that the trolley and weight hanger maintain a consistent load throughout the experiment. This can be achieved by keeping the total mass of the trolley and weight hanger unchanged and ensuring that no additional weights are added or removed during the experiment.

The student could improve the procedure by conducting the experiment on a smoother runway or by applying a lubricant to the wheels of the trolley to reduce friction. Alternatively, they could measure the force of friction and subtract it from the total force to accurately determine the net force acting on the trolley. This adjustment would help in accurately measuring acceleration attributable solely to the applied forces.

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. When Q collides with R, the momentum lost by Q is equal to the momentum gained by R. Therefore, the total momentum before the collision is equal to the total momentum after the collision. In mathematical terms, if the momentum is defined as the product of mass and velocity, then:

$ext{Momentum} = m imes v$

The conservation of momentum in this case can be expressed as:

$m_Q v_{Q_{initial}} + m_R v_{R_{initial}} = m_Q v_{Q_{final}} + m_R v_{R_{final}}$