# What is the power?

## Homework Statement

The brakes of a 1452 kg car bring it to a stop from a speed of 17.2 m/s in a distance of 100 m. If the car originally stops in 6.2 s (100 m), what power is developed by the brakes?

W = FF Δs
W = ½ m· v^2
P = W/t
P = F * v

## The Attempt at a Solution

W = 1/2 * m * v^2
W = 1/2 * 1452 kg * 6.2 s ^2
W = 214779.84 J

P = W/t
P = 214779.84 J/6.2 s
P = 4501.2 W

I know that this isn't correct because it is a multiple choice study guide. The options are the following:

a. 230 kW
b. 34.7 kW
c. 23.4 kW
d. 2.15 kW

It is the only problem I can't solve, and I'd like to know how to! Thank you.

## Answers and Replies

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PhanthomJay
Homework Helper
Gold Member

## Homework Statement

The brakes of a 1452 kg car bring it to a stop from a speed of 17.2 m/s in a distance of 100 m. If the car originally stops in 6.2 s (100 m), what power is developed by the brakes?

W = FF Δs
W = ½ m· v^2
P = W/t
P = F * v

## The Attempt at a Solution

W = 1/2 * m * v^2
W = 1/2 * 1452 kg * 6.2 s ^2
v= 17.2
W = 214779.84 J
yes..
P = W/t
P = 214779.84 J/6.2 s
P = 4501.2 W
but 214780/6.2 = 34,700 watts. Just check your math. You were putting in wrong numbers or dividing incorrectly, or both......