1.22 Use the conservation of momentum to calculate the mass, velocity or momentum of objects.

Conservation of momentum means that momentum is conserved if it is not disrupted by external forces.

momentum at the start = momentum at the end

For this, you would use the equation:

Momentum = Mass x Velocity
P = M x V
(momentum measured in kg m/s, mass in kg and velocity in m/s)

Eg: Two cars are on the same road, moving in the same direction. Car 1 has a mass of 2000kg and Car 2 has a mass of 1000kg, moving at 20 m/s. Car 1 is stationary.

a) How much momentum does each car have (at the start?)
b) What is the momentum at the start?
c) What is the momentum of each car after the crash? 

a ) Car 1

P = M x V

= 2000 x 0

= 0 kg m/s

Car 2

P = M x V

= 1000 x 20

= 20,000 kg m/s

b) The momentum at the start would be the momentum of Car 2; 20,000 kg m/s

c) Momentum at the start = momentum at the end

Car 1 now was hit with 20,000 kg m/s of momentum while car 2's momentum dropped to ZERO.