# A car requires a constant power of #50# #hp# to maintain a constant velocity of #10# #ms^-1# (about #36# #kmh^-1#). What is the magnitude of the net force impeding motion (friction plus air resistance)?

##### 1 Answer

Converting the power from hp to kW and dividing by the velocity (see the explanation below for why we do that) we find that the net force resisting motion is

#### Explanation:

Our first step is to convert horsepower

There are a few logical steps to get to our answer:

Power is defined as the rate at which work is done: the amount of work done per second:

The work done is the applied force times the distance traveled:

Substituting this into the first equation above, we get:

But distance over time is just velocity,

Rearranging to make

Substituting in the information we have:

In this case, the mass of the car is unneeded information in the question: the net force resisting motion is