4 (a) Which of these is a unit of momentum? A kg/m/s B kg/m/s C kg/m/s² D kg/m/s² (b) Students investigate conservation of momentum using two identical trolleys - Edexcel - GCSE Physics: Combined Science - Question 4 - 2022 - Paper 1

To investigate momentum conservation, the students can set up a track with two identical trolleys, A and B, positioned at opposite ends. Trolley A can have a card attached, which adds mass. The students will release trolley A from rest and let it collide with trolley B, which is stationary. They can use a motion sensor to measure the velocity of both trolleys before and after the collision. By calculating the momentum of each trolley before and after the collision, the students can compare the total momentum to verify that it remains constant, thus demonstrating the conservation of momentum.

The slope of the runway allows trolley A to gain speed as it rolls down, ensuring that it collides with trolley B with sufficient velocity, consistent with the requirements of the experiment.

To calculate the average force exerted by the ball on the racket, we use the formula: $F = \frac{mv - mu}{t}$. Here, m = 0.075 kg, v = 15 m/s, u = -8.2 m/s (opposite direction), and t = 0.012 s. Substituting the values gives:

$F = \frac{(0.075 \times 15) - (0.075 \times -8.2)}{0.012}$

Calculating this results in: $F = \frac{(1.125 + 0.615)}{0.012} = \frac{1.740}{0.012} \approx 145 N.$

Newton's Third Law of Motion states that for every action, there is an equal and opposite reaction. In this collision, when the racket applies a force on the ball to hit it, the ball simultaneously applies an equal and opposite force on the racket. This interaction illustrates the concept of action and reaction forces acting on different bodies during the collision.