Electricity. I took something like this hope this helps :)
Actually the question is not clear. The Benefit of lifting using lever is that you can apply force in a convenient direction and you can use very less force to lift object by balancing the torque due to object.For example you want to lift a mass of 4N with a force 2N you can use a class 2 lever and maintain the ratio between the distances of the body and the point of application of force from the fulcrum to be 1:2.In any case balance the torque to get the required force.
We can solve the problem by using the law of conservation of energy.
Initially, the rock has only gravitational potential energy, which is given by
where mg is the weigth of the rock (2200 N), while h is the height at which the rock has been released (h=15 m). If we calculate it, we get
Just before hitting the ground, the rock height is zero, so its potential energy is now zero. So the total mechanical energy of the rock now is just kinetic energy:
however, the mechanical energy of the rock must be conserved, so
and so we have that the kinetic energy of the rock just before hitting the ground is equal to its initial potential energy:
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