Collisions Practical Report
by Kobi Snow-Abeyratne
To investigate whether total momentum is conserved during a collision.
Two dynamics trolleys
Several 1 kg masses to add to the trolleys
Two rubber bands tied together that will stretch to 20 cm quite easily
Level bench top
Piece of A4 paper
The piece of A4 paper was attached to the bench top with masking tape. Two parallel lines were ruled, 20cm apart.
The two trolleys were linked with the rubber bands.
The trolleys were pulled apart and their front ends were held on the two lines.
The trolleys were released. The trolleys accelerated towards each other and collided at the same time. The distance the trolleys travelled in the given time was proportional to their relative velocities. The place where the trolleys collided were determined and the collision point was marked on the paper.
The distance was measured from one line to the collision point (d1) and the same for the other line (d2). As the trolleys both collided at the same time, there was no need to measure the times as the distances were proportional to the collision speeds.
Various masses to one (or both) of the trolleys were added and the experiment was repeated. Approximately five different mass combinations were tested.
WITHOUT ADDED MASS
m1 = 0.2kg
d1 = 0.13m
m1 x d1 = 0.026
m2 = 0.2kg
d2 = 0.07m
m2 x d2 = 0.014
(m1 x d1) - (m2 x d2) = 0.026 - 0.014 = 0.012
WITH ADDED MASS
m1 = 0.2kg (trolley) + 0.5kg (weights) = 0.7g
d1 = 0.11m
m1 x d1 = 0.077
m2 = 0.2kg (trolley) + 0.5kg (weights) = 0.7g
d2 = 0.09m
m2 x d2 = 0.063
(m1 x d1) - (m2 x d2) = 0.077 - 0.063 = 0.014
When the trolleys are released there are a variety of factors that determine whether both trolleys will travel towards each other for the same period of time. This can occur if both trolleys have the same velocity, distance apart, weight, acceleration and release time. The magnitude of the force acting on each trolley should also be the same if they have the same acceleration and same mass, which should occur if an equal amount of weights were added and the trollies were released at the same time from the same distance.
As both trolleys were not moving at the end after the collision they would have no momentum (0 kg m/s). According to the results the initial total momentum of the system without the added mass was 0.012 kg m/s and with the added mass the ITM was 0.014 kg m/s.