Question

A body of mass $m$ is in vertical motion under the influence of gravity then

• A. work will be negative and kinetic energy increases during fall.
• B. kinetic energy decreases when body is projected up and work will be negative.
• C. kinetic energy increases when body is projected up and work will be positive.
• D. work will be positive and kinetic energy decreases during fall.

Answer 1

The correct option is B kinetic energy decreases when body is projected up and work will be negative.

i) Vertical motion, body projected up

The motion of the body and the direction of gravitational force will be in the opposite direction. So work done will be negative. As the body moves upward, it's velocity decreases hence the kinetic energy too.

ii) Body falling down.

The motion of the body and the direction of gravitational force would be in the same direction, so the work done by gravity is positive. The body gains velocity as it reaches earth's surface, hence the kinetic energy increases.
Option B.