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Homework Help: Find the speed of a Block going up an incline

  1. Oct 18, 2015 #1
    1. The problem statement, all variables and given/known data
    What is the speed after 5 seconds?
    Box1 : 400 kg
    Box2: 100 kg
    Initial velocity: 20 m/s
    μk: .30
    Angle of Incline: 25
    Time: 5 seconds
    2. Relevant equations
    Force of Friction: (mg)(cos θ)(μ)
    Effective Gravity: (mg)(sinθ)
    Vf = Vi + at
    3. The attempt at a solution
    For Force of friction I got 1066.9055
    For Effective Gravity I got 1658.3540
    Then I added the weight from the 100 kg block

    Then I did Fnet = -1066.91-1658.35 + 981 = 500a
    a = -3.49

    Vf = Vi + at
    Vf = 20 + (-3.49)(5)
    Vf = 2.55

    I'm not sure if this is correct
  2. jcsd
  3. Oct 18, 2015 #2


    User Avatar

    Staff: Mentor

    Hi Lucy90,

    Welcome to Physics Forums.

    Your numerical result looks fine, but the units are missing. Always be sure to include the units on numbers that are results (including intermediate results). It helps with checking, and markers will usually deduct points (or simply mark the answer wrong) if they are left out. It's good to get into the habit of always including them.
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