2.4 Momentum & Impulse

A film stuntman, of mass 85.0 kg, is being trained to jump off high objects. 

In one scene he steps off a roof and falls vertically to the ground below. Just before he hits the ground he has a velocity of 9.08 m s⁻¹. After he has landed on the ground he remains at rest.

When the stuntman keeps his legs fully rigid, the time for the impact is 4.20 ms. 

A bullet, of mass 20 g, leaves the barrel of a rifle, of mass 1.9 kg, with a momentum 4.0 kg m s⁻¹.

The bullet has a momentum of 3 kg m s⁻¹ just before it hits a target. It takes 0.0025 s for the bullet to be stopped by the target. 

Zorbing is an activity which involves a person running inside an inflatable ball, called a ‘zorb’.  Two zorbs, A and B, collide head on with each other, as shown.  The total mass of zorb A and its occupant is 75 kg and the total mass of zorb B and its occupant is 60 kg.  Before the collision, zorb A is travelling at 2.0 m s⁻¹ and zorb B is travelling at 1.5 m s⁻¹.

After the collision, both zorbs bounce off each other and move in opposite directions, as shown below. Zorb A travels at 0.8 m s⁻¹ and zorb B travels at 2.0 m s⁻¹.

A collision can be described as being elastic or inelastic. When there are no external forces acting on the collision.

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During a safety test, a car of mass 1250 kg travels at 0.5 m s⁻¹ towards a wall.

The car has a force sensor attached to the bumper which detects the force exerted on the front of the car.  The graph below shows the variation of force with time for the duration of the collision.

All cars are designed with a crumple zone to protect passengers if they are involved in a collision.