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Homework Help: Physics-dynamics question with incline?

  1. Mar 14, 2010 #1
    No matter how many times i do it, i seem to be doing something wrong :|

    1. The problem statement, all variables and given/known data
    A wet bar of soap (150 g) slides without friction down a ramp (2.0 m) long inclined at 7.3degrees. How long does it take to reach the bottom? Neglect friction.
    & How would this change if the soaps mass were 250 grams?

    2. Relevant equations

    stated below>>

    3. The attempt at a solution
    So i tried to calculate Fnet using sine.
    since Fg=1.5kg*9.8=14.7N
    Then i did, sin7.3=x(aka fnet) / 14.7
    x = 12.5

    Then: Fnet = ma
    12.5=0.15a
    a=83.3

    then
    d=vit+1/2at^2
    2=0+1/2(83.3)t^2
    2/(1/2*83.3)=t^2
    Suqareroot(0.048)=t
    t=0.219 or around there.

    However the answer is 1.8 seconds?
    Can anyone help me see what im going wrong?

    Any help is much appreciated, thanks.


    EDIT:::
    Sorry, nevermind, turns out my calc was in radian mode -facepalm- Good grief.
     
    Last edited: Mar 14, 2010
  2. jcsd
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