Question

A body of mass $2kg$ is dropped from a height of $1m$. Its kinetic energy as it touches the ground is (assume $g=9.8m{s}^{-2}$)

• A. $19.6$ $N$
• B. $19.6$ $J$
• C. $19.6$ $kg$
• D. $19.6$ $m$

Answer 1

The correct option is B $19.6$ $J$

Given,
mass of the ball (m) $=2kg$
height from the ground (h) $=1m$
Initially, the ball possesses only potential energy.
Potential energy $=mgh$
Potential energy $=2\times 9.8\times 1=19.6J$
As we know, all the potential energy of the ball will convert into kinetic energy as soon as the ball hits the ground.
Hence, Kinetic energy $=$ Potential energy $=$ $19.6J$
Note that $N$ is the unit of force, hence $19.6N$ would be incorrect. Similarly for the others.