Explain how a large force is exerted on a passenger in a vehicle in the event of a car crash and how this can be reduced.

Using idea of conservation of impulse-momentum theorem, the instantaneous velocity times mass is equal to force times the change in time.

mv = Ft

To reduce the force, decrease the velocity and mass. You can also extend the time of the collision. This is why cars collapse on impact. They were design that way to reduce the force on the car and the passenger.

Hopes this helps!