Question

Scientists test the safety features of a car by crashing it into a large block of concrete. A crash test dummy sits in the driver's seat. A video camera records the crash. In one test, the car is travelling at 13 m/s and the dummy has a mass of 83 kg.

a)Calculate the momentum of the dummy.

b)In another test, the momentum of the dummy changes by 1250 kg m/s in a time of 0.17 s.
Calculate the average force acting on the dummy during this time.

c)These tests help to make our roads safer. Use ideas about momentum to explain how seat belts and the crumple zones of a car help to reduce injuries during a crash. ​

Answer 1

The momentum of the dummy is 1079 kg m/s, and the average force acting on the dummy during the crash is 7352.94 N. Seat belts and crumple zones reduce injuries by increasing the time over which a crash occurs, thus lowering the average force experienced by passengers.

Step-by-step explanation:

a) To calculate the momentum of the dummy, you use the formula p = mv, where p is momentum, m is mass, and v is velocity. The dummy has a mass of 83 kg and is traveling at 13 m/s, so the momentum p is:

p = 83 kg × 13 m/s = 1079 kg m/s.

b) To calculate the average force acting on the dummy, we need to use the change in momentum (Δp) and the time over which the momentum changes (Δt). The force is calculated using the formula F = Δp / Δt. Given the change in momentum is 1250 kg m/s and the time is 0.17 s, the force F is:

F = 1250 kg m/s ÷ 0.17 s = 7352.94 N.

c) Seat belts and crumple zones are safety features that make use of the conservation of momentum to reduce injuries during a crash. Seat belts spread the force over the body and increase the time it takes for the body to come to a stop, thus reducing the average force experienced by passengers. Crumple zones are designed to absorb kinetic energy and increase the time it takes for the car to come to a complete stop, thereby reducing the forces on the occupants.