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Homework Help: Pls. help -> acceleration

  1. Aug 20, 2007 #1
    pls. help --> acceleration

    1. The problem statement, all variables and given/known data
    a ball starts from rest and rolls down a hill with a uniform acceleration travelling 150m during the second 5.0s of its motion. How far did it roll during the first 5.0s of its motion:confused:

    pls. help

    2. Relevant equations


    3. The attempt at a solution
     
  2. jcsd
  3. Aug 20, 2007 #2
    what have u tried so far so that we can help u?
     
  4. Aug 20, 2007 #3
    i tried to get its acceleration and i got a 3m/s^2, but after that i dont know what to do, I'm not even sure if i got it right.
     
  5. Aug 20, 2007 #4
    What you have to see first is that the distance travelled by the rolling ball in the next 5 seconds is nothing but the difference between the distance travelled by the ball in 10 seconds and the distance travelled in 5 seconds.

    By the simple kinematic equation, we know that:

    S=ut+(1/2)at^2

    Since the initial velocity u is 0, the ut component of the equation goes and only (1/2)at^2 is left.So the distance travelled in the next 5 seconds is nothing but:

    (1/2)a{(10^2)-(5^2)}=150

    Solve for 'a'.(It wouldn't work out to 3m/s^2.)
    Now, u know 'a' so substitute it in the equation (1/2)a.5^2 to get the answer!
     
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