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Math Help - Power

  1. #1
    Member WhoCares357's Avatar
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    Power

    A 0.55 kg mass sliding on a horizontal frictionless surface is attached to one end of a horizontal spring (with k = 475 N/m) whose other end is fixed. The mass has a kinetic energy of 15.0 J as it passes through its equilibrium position (the point at which the spring force is zero).
    Part 1:
    At what rate is the spring doing work on the mass as the mass passes through its equilibrium position?
    I know the answer to this is 0W, but I have no idea how to get it.

    Part 2:
    At what rate is the spring doing work on the mass when the spring is compressed 0.126 m and the mass is moving away from the equilibrium position?
    I don't know how to find the velocity of the object. I can find F with F=-kx, but I need velocity to complete the equation for Power=F*v.
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  2. #2
    MHF Contributor
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    Quote Originally Posted by WhoCares357 View Post
    Part 1:


    I know the answer to this is 0W, but I have no idea how to get it.

    Part 2:


    I don't know how to find the velocity of the object. I can find F with F=-kx, but I need velocity to complete the equation for Power=F*v.
    HI

    For (1)

    you are told that when the object is in equilibrium position , the force of the spring exerted on the mass is 0 which also suggests that the work done on the mass is 0 (W=fs) , then it follows that power is also 0

    For (2) , the elastic potential energy equals the kinetic energy of the mass from the principle of conservation of energy .

    \frac{1}{2}kx^2=\frac{1}{2}mv^2
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