Chapter - 4 Work and Energy

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Work and Energy


An object of mass 40 kg is raised to a height of 5 m above the ground. What is its potential energy? If the object is allowed to fall, find its kinetic energy when it is half-way down.


In the above question it is given that:

h = Vertical displacement = 5 m

m = Mass of the object = 40 kg

g = Acceleration due to gravity = 9.8 m/s²

Gravitational potential energy is given by the expression,

W = mgh

W = 40 	imes 5 	imes 9.8 = 1960 J

At half-way down, the potential energy of the object will reduce to half.

P.E. at half-way down = frac{1960}{2} = 980 J

At this point, the object has potential energy equal to kinetic energy. This is due to the law of conservation of energy.

Hence, half-way down the kinetic energy of the object will be 980J.

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