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Forces and Motion

Momentum - What is an Inelastic Collision?

Click here to see the difference
between an elastic collision and an inelastic collision.

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.
Car 2 has a mass of 800 kg and is stationary.
Car 1
collides with car 2 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
= 1200 x 20
                        = 24000 kgm/s.

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

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

The law of 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 calculated because
momentum before = momentum after
           24000 = 2000 x v

v = 24000 ÷ 2000
= 12

The total kinetic energy decreases with an inelastic collision.

You can use the equation for kinetic energy
to see that the total kinetic energy
the collision is 240,000J
and after the collision it is 144,000J

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