Conservation of Momentum & Energy

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.

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