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Work done by a variable force

  1. Nov 4, 2014 #1
    A 1.2 kg block is held against a spring of force constant 1.0 x 10^4 N/m, compressing it a distance of 0.15m. How fast is the block moving after it is released and the spring pushes it away?
     
  2. jcsd
  3. Nov 4, 2014 #2
    think about conservation of energy, and the potential energy stored in the spring before release
     
  4. Nov 4, 2014 #3
    i know that k=1.0 x 10^4
    x(final)=-0.15
    x(initial)=0
    work=1/2kx^2= -112.5

    but i dont know how to find the velocity

    i tried using v^2=k/m (x^2)
    and recieved 13.69m/s
     
  5. Nov 4, 2014 #4
    Do you think that's wrong?
    You solved for v. v is the velocity. well technically the speed here, but I'd assume that's what your teacher meant.
     
  6. Nov 5, 2014 #5
    Looks good, average force seems to satisfy.
     
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