Question

At a particular height, the velocity of an ascending body is $\overrightarrow{u}$. The velocity at the same height while the body falls freely is

• A. $2\overrightarrow{u}$
• B. $-\overrightarrow{u}$
• C. $\overrightarrow{u}$
• D. $-2\overrightarrow{u}$

Answer 1

Answer: (B)

$-\overrightarrow{u}$

The body has kinetic energy equal to $\frac{1}{2}m{u}^2$ while ascending. This kinetic energy keeps on decreasing as the potential energy increases while ascending, in accordance with the law of conservation of energy.

While descending, the opposite happens. The gravitational potential energy converts back to kinetic energy. When the body reaches the same height again, the gravitational potential energy is same as that earlier, and again the kinetic energy becomes $\frac{1}{2}m{u}^2$, however the direction of velocity is reversed.

Hence correct answer is option B.