Forces and Motion

Momentum - Inelastic Collision - Calculations.

To understand the difference between an elastic collision
and an inelastic collision, click here.

An example of an inelastic collision
is where one car collides with another
and both cars keep moving but stick together after the collision.

For example, car 1 has a mass of 1200 kg and travels with a velocity of 20 m/s.
It collides with car 2 which has a mass of 800 kg and is stationary
and they both stick together.
What is the velocity of both cars after the collision?

The total momentum before the collision is

momentum = mass x velocity

For car 1
momentum = 1200 x 20
                        = 24000 kgm/s.

For car 2
momentum = 800 x 0
                    = 0 kgm/s.

Total momentum before the collision is
24000 + 0 = 24000 kgm/s.

The conservation of momentum tells us that
the total momentum after the collision is also 24000 kgm/s.

The mass of both cars after the collision is
1200 + 800 = 2000 kg.

The velocity of both cars after the collision can be found because
momentum before = momentum after
           24000 = 2000 x v

v = 24000 ÷ 2000
= 12 m/s.

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