The gravitational potential energy of an object depends on its weight and how far it moves vertically.
Ep = m x g x h

Seat belts and air bags spread the force across the chest and they also increase the impact time.
Side impact bars and crumple zones 'give way' in an impact so increasing the impact time.
We can use the conservation of momentum to find the speed of a car before an impact.

The kinetic energy of a moving object depends on its mass and its speed.
Ek = 1/2 x m x v2.
Elastic potential energy is the energy stored in an elastic object when work is done on the object.

p = m x v
The unit of momentum is kg m/s.
Momentum is conserved whenever objects interact, provided no external forces act on them.

Momentum = mass x velocity; and velocity is speed in a given direction.
When two objects push each other, they move apart:
-with different speeds if they have unequal masses.
-with equal and opposite momentum so their total momentum is zero.

Work is done on an object when a force makes the object move.
Energy transferred = work done.
W = F x d.
Work done to overcome friction is transferred as energy that heats the objects that rub together and the surroundings.

When vehicles collide, the force of the impact depends on mass, change of velocity and the duration of the impact.
When two vehicles collide:
-they exert equal and opposite forces on each other
-their total momentum is unchanged