The following is part of a student’s report on an experiment to verify the principle of conservation of momentum - Leaving Cert Physics - Question 1 - 2014

The student measured:

• The masses of both bodies (A and B).
• The time, through gaps, for body A to pass through a light gate, which gives an average time.
• The length of gaps between the light gates to calculate distance.

These measurements were combined to calculate velocities using the formula: ext{Velocity} = rac{ ext{Distance}}{ ext{Time}}

Using the data provided:

1. Calculate the momentum before the collision:

   • Momentum of body A before collision: $p_A = m_A imes v_A = 0.3251 ext{ kg} imes 0.84 ext{ m s}^{-1} = 0.273 ext{ kg m s}^{-1}$
   • Body B is at rest, so its momentum is 0.
   • Total momentum before = $0.273 ext{ kg m s}^{-1}$.

2. Calculate the momentum after the collision:

   • Total mass of A and B after the collision: $m_{total} = 0.3251 ext{ kg} + 0.3498 ext{ kg} = 0.6749 ext{ kg}$
   • Velocity of A and B together after collision: $p_{AB} = m_{total} imes v_{AB} = 0.6749 imes 0.41 = 0.277 ext{ kg m s}^{-1}$

3. This shows that momentum is conserved if the total momenta before and after the collision are equal, taking into account experimental errors.

The two forces to consider are:

1. Weight (gravitational force) acting downwards on the bodies.
2. Friction (between the bodies and the track).

To reduce the effects of these forces, the student could:

• Weight: Ensure that the apparatus is level and indeed that weight does not affect the motion. If necessary, use a light-weight setup that minimizes gravitational influence.
• Friction: Use a smooth, well-lubricated track or low-friction wheels to minimize the effect of friction.