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Homework Help: Find how much a wire stretched at the bottom of swing of pendulum

  1. Feb 18, 2012 #1
    1. A building is to be demolished by a 400kg shell ball swinging on the end of a 30.0 m steel wire of diameter 5.00 cm hanging from a tall crane. As the ball is swung though an arc from side to side, the wire makes an angle of 50° with the vertical at the top of the swing. find the amount by which the wire is stretched at the bottom of the swing



    2. stress=F/A, strain=ΔL/L, F=ma, Y= Young's Modulus



    3. ΔL=F/A*L/Y
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Feb 19, 2012 #2
    I suppose you have the problem at finding the force. User Energy conservation to find the velocity at the lowermost point. Then use the equation T-mg = mv^2/(L+ΔL)
     
  4. Feb 19, 2012 #3
    vivek, let the guy show some work at least. thats the forum policy. the person has not shown ANY work.
     
  5. Feb 19, 2012 #4
    i figured out all these values and plugged them into the eqn i have:

    A=1.96E-3 m^2 wire
    Y=20E10
    L=30m
    Tension if it were at rest and bottom: T=mg=3924N
    and got dL=0.03cm
    but i'm assuming at it stretches the same if it were at rest or accelerating when at the bottom
    how do i take acceleration into account?
     
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