Assessment Problems 2

NASAPhysics

Online Course

Conservation of Momentum & Energy

Assessment Problems

1. The kinetic energy of a race car is x Joules. What would be the kinetic energy of the race car if its mass were doubled and the speed remained constant?

Answer: Since KE = ½ mv², doubling the mass would double the KE.
2. The kinetic energy of a truck is x Joules. What would be the kinetic energy of the truck if its speed doubled?

Answer: The KE of the truck varies with the square of the velocity. Doubling the speed would increase the KE by a factor of 4.
3. Explain how air bags help in preventing injury during a crash.

Answer: In a crash, the time to reduce the car’s speed to zero is very short and the force is large. An air bag allows the passenger’s head to come to rest over a longer period of time, thus reducing the size of the force.