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Homework Help: What is the power?

  1. Mar 29, 2010 #1
    1. The problem statement, all variables and given/known data
    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?

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

    3. 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.
  2. jcsd
  3. Mar 29, 2010 #2


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    v= 17.2
    but 214780/6.2 = 34,700 watts. Just check your math. You were putting in wrong numbers or dividing incorrectly, or both......
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