Question

A young man in good physical shape finds that his car is out of gas and 1 mile from a gas station. He decides to push the car to the gas station. The force of rolling friction against the car is 50 lbs which is about 225 N.   He will push with this much force all the way to the gas station. The air drag force is negligible since the speed of the car through the air will be very small.

Useful information:   1 food calorie = 1 kcal = 4200 J      1 mile = 1609 m 1 hp = 746 watts

a) How many joules of useful work does the man do?

b) If he can push the car 1 mile in 30 minutes, what is his power output in watts? In horsepower?

c) The human body is 1/6 inefficient in terms of converting food energy to useful work. That is, for every 6000 J of food energy consumed, your body can only do 1000 J of useful work. The other 5000 J would turn into body heat. After pushing the car, the young man decides to replenish the food energy he has used with Hershey bars. If a Hershey bar contains 210 food calories, how many Hershey bars does he eat?

Answer 1