**AP Physics 1 Question 389: Answer and Explanation**

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**Question: 389**

**7.** A car with a mass of 1000 kg experiences a frictional force of 3500 N while driving at a constant speed of a 15 m/s. What is the power output of the car's engine?

- A. 3.5 kW
- B. 5.25 kW
- C. 35.0 kW
- D. 52.5 kW

**Correct Answer:** D

**Explanation:**

**D**

In order to maintain a constant speed, the net force on the car must be zero. This means that the car's engine must be applying a force equal in magnitude but opposite in direction to the frictional force. The equation *P* = *Fv* then yields

*P* = *Fv* = 3500 N ยท 15 m/s = 52,500 W = 52.5 kW