Question

Consider the following situation:

An object is lifted up. Work is done by applied force and the object moves
upward. The force of gravity is also acting on the object.

a) Which force is doing positive work and why?

b) Which force is doing negative work and why?​

Answer 1

Explanation:

No,

When a body is lifted the force of gravity is acting in the downward direction. But, the displacement of the body is in the upward direction. Since the angle between the force and displacement is 0

0

.

We know

W=F×S×cosθ

So, the Work done will be positive .

Answer 2

Explanation:

(ii) The object is doing Negative Work. Because the angle between lifting the body and force of gravity is 180 degree. Thus, cos theta=cos 180 degree= -1. Hence, the work done by the boy is negative.

(i)) The force of gravity is doing positive work, because, the force pulls down and the value of theta is 0. So, cos theta=cos O degree=1. Thus, work done by force of gravity is positive .