# Suppose a car approaches a hill and has an initial speed of 108 km/h at the bottom of the hill.?

Suppose a car approaches a hill and has an initial speed of 108 km/h at the bottom of the hill. The driver takes her foot off of the gas pedal and allows the car to coast up the hill.

a.) If the car has the initial speed stated at a height of h = 0, how high, in meters, can the car coast up a hill if work done by friction is negligible?

b.) If, in actuality, a 710-kg car with an initial speed of 108 km/h is observed to coast up a hill and stops at a height 20.5 m above its starting point, how much thermal energy was generated by friction in J?

c.) What is the magnitude of the average force of friction, in newtons, if the hill has a slope 2.9° above the horizontal?

### 1 Answer

- 4 weeks ago
a.) kinetic energy of car = final potential energy. Solve for h.

b.) Find what the ideal value for the final height should be, find the difference between that final energy value and the example they give you. That is the heat due to friction.

c.) Work done by friction = energy lost by heat. Set part b answer equal to force*distance. You can find the distance the car traveled using trigonometry. Solve for F.