Question

An object of mass m is dropped from a height 'h'. If it strikes the ground with speed 0.8gh , then work done by air resistance is​

Answer 1

Answer:

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Answer 2

The correct question is:

An object of mass m is dropped from a height 'h'. If it strikes the ground with speed $0.8\sqrt{gh}$ , then work done by air resistance is​?

Given:

Mass of the object = m

Height from which the object is dropped = h

Speed with which the object strikes the ground = $0.8\sqrt{gh}$

To find:

Work done by air resistance.

Solution:

Here we have to conserve energy and form equations:

The initial potential energy when the object is at height h = Kinetic energy of object + work gone in conquering air resistance.

Let work required in conquering air resistance = A

Then:

mgh = mv²/2 + A

A = mgh - m*( $0.8\sqrt{gh}$)²

A = mgh - 0.64mgh

A = 0.36mgh

Therefore work done by air resistance will be 0.36mg in the opposite direction of the fall of the object.