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Work, Force, Brakes

  1. Sep 26, 2013 #1
    1. The problem statement, all variables and given/known data

    Use this information to answer the next 4 questions: 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.



    2. Relevant equations

    15. How much work do the brakes do?
    2.15 x 105 J
    1.42 x 106 J
    2.50 x 106 J
    7.12 x 105 J


    16. What average force do the brakes apply?
    2.50 x 104 N
    7.12 x 103 N
    2.15 x 103 N
    1.42 x 104 N


    17. How much distance would the car cover as it stops if the speed were doubled? Assume that the average braking force remains constant.
    400 m
    100 m
    200 m
    800 m


    18. If the car originally stops in 6.2 s (100 m), what power is developed by the brakes?
    23.4 kW
    2.15 kW
    34.7 kW
    230 kW



    3. The attempt at a solution
    I am so lost and I don't even know where to start with these. If you can help me I will be so grateful!!
     
  2. jcsd
  3. Sep 26, 2013 #2

    tiny-tim

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    Homework Helper

    hi laurenbaboran! :wink:

    let's start with #15:

    what is the definition of work done?

    what theorems do you know about work done?​

    one of those two answers should give you a quick way of answering #15 :smile:
     
  4. Sep 26, 2013 #3
    Just use the standard equations of kinematics.
    Calculate the acceleration of car first.
    Use it to find force.
    Use that to find work.
    :wink:
    (EDIT:crossed posts with tiny-tim and his shiny new avatar :smile:)
     
  5. Sep 26, 2013 #4
    Okey dokey thanks for the help :) Sorry to spam up the forum thread! I am SO bad at physics!
     
  6. Sep 26, 2013 #5

    tiny-tim

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    Science Advisor
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    No, that's what it's there for! :wink:

    Show us what you get :smile:
     
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