Energy is needed to apply force, force is needed to get work done, and work generates power.
Work is said to be done when force applied on a body causes displacement of the body in the direction of force.
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Power refers to the rate of work done by a force.
“Potential Energy” refers to “stored energy” whereas “kinetic energy” is energy due to motion. When an object moves, potential energy is converted into kinetic energy.
When you apply force, work may not be done, as per Physics!
A person does no work if there is no change in position or no motion even after the application of force. E.g. a boy pushing a heavy stone does no work if the stone does not move although he may get tired.
The work done by a force is zero if the body moves in the direction perpendicular to the direction of force. E.g. If a coolie moves on a plane road with luggage on his head, the work done by him against the force of gravity (weight) is zero. Since distance moved by him is normal to his weight.
Dissipation of Energy
While transformation of energy from one form to the other desired form, the entire energy does not change into the desired form, but a part of it changes either to some other undesirable form (usually heat due to friction) or a part is lost to the surroundings due to radiation which is not useful. This conversion of energy to the undesirable (or non-useful) form is called dissipation of energy. Since this part of energy is not available to us for any productive purpose, so we call this energy as the degraded form of energy.
Numerical Problems
Q: How much distance does a trolley move when a force of 350N does a work of 7000 J on it?
Solution: Given: Force, F = 350N
Work done, W = 7000 J, distance, s=?
W = F x s so s = W / F = 7000 J /350 N = 20m
So the distance moved by the trolley is 20m in the direction of force.
Q: How high should a hammer of mass 3 kg be raised, so that it acquires a potential energy of 45 J. (take force of gravity on a mass of 1 kg is 10 N).
Solution: Given: m=3kg, g=force of gravity on a mass of 1 kg is 10 N, P.E.=45J.
PE = mgh, h=45/30 = 1.5m.
So the hammer should be raised to a height of 1.5m.
Q: A water pump is used to draw 80 kg of water from a 40 m deep well in 8s. When the force of gravity on 1 kg of water is 10N find: a. work done by the pump. b. potential energy stored in the water. c. power spent by the pump.
Solution: Given: m=80kg, g=10N, h=40m, t=8s
a. Work done by the pipe = force x distance = 80x10x40 (force=mg) = 32000J
b. potential energy stored in the water = mgh = 80x10x40 = 32000J
c. power spent by the pump = P=W/t = 32000/8 = 4000W
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