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Homework Help: Find the acceleration of the object

  1. Mar 15, 2010 #1
    please open the word document.
    This questions really frustrating me
     

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  2. jcsd
  3. Mar 15, 2010 #2

    rl.bhat

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    Re: Incline

    You can find the acceleration of the object by using
    vf^2 = vi^2 + 2*a*s. vi and s is given. Find a.
    This acceleration has two components. One the component of g which acts in the downward direction. And the other due to braking force, which acts in the opposite direction of the motion. In the diagram sinθ is given. (10/100).
    Write down the expression for the acceleration and solve the problem..
     
  4. Mar 15, 2010 #3
    Re: Incline

    um to find acceleration cant you use a=gsinθ, but if you use that its 10xsin(5.740) which equaks 1.001 because if sinθ=10/100 then θ=5.74. However if I use your equation i get a=4.5m/s/s
     
  5. Mar 15, 2010 #4

    rl.bhat

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    Re: Incline

    The acceleration a is correct.
    Now a = af - g*sinθ, where af is the acceleration due to frictional force.
     
  6. Mar 15, 2010 #5
    Re: Incline

    how do i calculate af?
     
  7. Mar 15, 2010 #6

    rl.bhat

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    Re: Incline

    In the problem they have asked
    What is the constant braking force?
    So you have find af, then the braking force = m*af.
    You have found a and g*sinθ. Using the above equation find af.
     
  8. Mar 15, 2010 #7
    Re: Incline

    so is af = 4.500 - 1.001?, then the braking force is 1000*3.499=3499???????????????
     
  9. Mar 15, 2010 #8
    Re: Incline

    so then what is the driving force?
     
  10. Mar 15, 2010 #9
    Re: Incline

    is it just 1000N?
     
  11. Mar 15, 2010 #10

    rl.bhat

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    Re: Incline

    This step is wrong.
    af = a + g*sinθ.
    Αnd what do you mean by driving force?
    Sledge moves down due to gravitational force. The frictional force stops it.
     
  12. Mar 15, 2010 #11
    Re: Incline

    whats the difference between a and gsinθ?
     
  13. Mar 15, 2010 #12

    rl.bhat

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    Re: Incline

    mg*sinθ ......> Force acting on the sledge due to gravity in the downward direction
    μ*mg*cosθ.......>Frictional force in the upward direction = m*af
    Net retarding force acting on the sledge is
    mg*sinθ - m*af = - m*a.
     
  14. Mar 15, 2010 #13
    Re: Incline

    ok we calculated before that gsinθ = 1.001. so thats the acceleration downwards direction. then we calculated a to be 4.500 using that equation. why are they different when there both acceleration?
     
  15. Mar 15, 2010 #14

    rl.bhat

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    Re: Incline

    When you are using the equation vf^2 = vi^2 + 2*a*s. to find a, you are getting the acceleration -4.5 ms^-2. whereas g*sinθ +1. There directions are different.
     
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