Posted by **Gullu** on Thursday, August 18, 2011 at 8:12pm.

Two cars travel at the same speed, so that they move 105 km in one hour. One car, a sleek

sports car, has a motor that delivers only 35 kW of power at this speed. The other car

needs its motor to produce 65 kW to move the car this fast. The difference is caused by air

resistance.

a. For each car, list the external horizontal forces exerted on it, and give the cause of each

force. Compare their magnitudes.

b. By Newton’s third law, the car exerts forces on the ground and the air. What are their directions?

c. Calculate the magnitude of the forward frictional force exerted by each car.

d. The car engines did work. Where did the energy come from?

- Physics -
**bobpursley**, Thursday, August 18, 2011 at 8:51pm
a. Consider surface friction, and air friction.

b. the car tire tries to push the earth back, and the earth resists equal and opposite.

d. Duh, chemical?

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