Question

An object has a mass of 16 kg. It is 18 meters high, from the ground. It begins to fall, from rest, with kinetic friction due to air resistance. The heat generated by kinetic friction is 12 percent (12%) of its initial mechanical energy. Determine the speed of the object when its height is 11 meters.

Answer #1

From work enrgy theorem; work done by all the forces = change in Kinetic Energy (KE).

Initial mechanical energy = mgh = 161018 = 2880J

Heat generated by kinetic friction = 0.122880 = 345.6J, this will be equal to the magnitude of work done by friction.

Work done by gravity in falling to height of 11m = mgh = 1610(18-11)=1120J

(work done by gravity)+(work done by friction) = change in KE

1120 + (-345.6) = Final KE (as initially KE=0)

speed of object when it is at a height of 11m from the ground is
9.84m/s

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