Question

A body is projected upwards with a kinetic energy of $100J$. Taking the friction of air into account, when it returns on earth, its kinetic energy will be:

• A. more than $100J$
• B. less than $100J$
• C. $100J$
• D. none of these

Answer 1

The correct option is B less than $100J$

Kinetic energy $=\frac{1}{2}m{v}^2$
When the body returns to the earth its velocity will decrease due to friction of air i.e. some energy is lost in overcoming the friction. Thus, now its kinetic energy is less than $100J$.