Q. 134.3( 25 Votes )

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 (g = 10 m/s2)

Answer :

Given,

Mass, m = 40 kg


Acceleration due to gravity, g = 10 m/s2


Height, h = 5 m


We know that,


Potential energy = m × g × h


= 40 × 10 × 5


= 2000 J


When the object is fall to its half way down, then its height above the ground =


=2.5 m


Now, Potential energy = m × g × h


= 40 × 10 × 2.55 J


= 1000 J


Now, we know that according to the law of conservation of energy:


Total potential energy = Potential energy at half way down + Kinetic energy at half way down


2000 = 1000 + Kinetic energy at half way down


Kinetic energy at half way down = 2000 – 1000


= 1000 J

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