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A rock of mass 50kg is held at 45meter from the ground.it is allowed to fall freely.find the change in potential energy,when it is a height at 20meter from the ground.also find the speed at this time and kinetic energy ?

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    Ek + Ep = Epmax=mg*hmax=490*45=22,050 J.
    0 + Ep = 22,050 @ hmax(45m).

    Ep = mg*h = 490*20 = 9800 J. @ 20 m.
    Change in Ep = 22,050-9800 = 12,250 J.

    Ek + 9800 = 22,050
    Ek = 22050 - 9800 = 12,250 Joules @ 20m.

    Ek = 0.5m*V^2 = 12,250.
    25*V^2 = 12,250
    V^2 = 490
    V = 22.1 m/s.

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