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Pushing a Porsche

 Making a rest stop at a service station on the highway, the driver of a pickup truck turned off his truck, left it in neutral, and ran into the building, forgetting to set his emergency brake. Unfortunately, he was parked on a slight incline and the truck started to roll down. When the truck got to the bottom of the incline, the road was flat and smooth and the truck rolled on without slowing significantly. After traveling a short distance, it ran into a Porsche.   The driver of the Porsche also had left her car in neutral without setting the emergency brake. (Bad idea!) The truck was going pretty slowly and had a rubber bumper so when it hit the car, the car bounced off doing some damage, but not totaling the car. For the period of the collision, friction with the ground was negligible.

Here are the parameters of what happened.

• Distance van traveled after coming off the incline before it hit the car = 37 ft.
• Mass of the van = 2000 kg.
• Mass of the car = 1000 kg.
• Time car and truck are in contact = 1.5 s.
• Van's speed just before it hit the car = 10 km/hr.
• Van's speed just after the car and van separate = 5 km/hr.

a) What was the speed of the car after the collision? Explain how you know.

b) Is the information given enough to calculate the average force felt by the car? If so, calculate it. If not, explain why not.

c) Is the information given enough to calculate the average force felt by the truck? If so, calculate it. If not, explain why not.

d) How much mechanical energy was lost in the collision, if any? (This will determine how much damage the bumpers suffered.)

Page last modified January 29, 2008: P&E26