This question was previously asked in

DSSSB JE ME 2019 Official Paper Shift - 2 (Held on 06 Nov 2019)

Option 4 : 20 m/s

__Concept:__

The energy possessed by a body by virtue of its motion is called kinetic energy.

\(KE = \frac{1}{2}m{v^2}\)

Where m = mass of the body and v = velocity of the body

Potential energy (PE):

The energy possessed by a body by virtue of its position or configuration is called potential energy.

\(PE = mgh\)

Where, m = mass of the body, g = acceleration due to gravity and h = height of the body

Conservation of energy:

- According to the conservation of energy, energy can’t be created or destroyed, it can only transform from one form to another.
- The total energy of the system remains constant i.e. the sum of kinetic energy + potential energy remains constant.
- When a ball is falling freely then its initial potential energy will slowly get converted into kinetic energy. but the total energy will remain constant.
- Thus the potential energy will decrease and the kinetic energy will increase until the body reached the bottom.

__Calculation:__

__Given:__

h = 20 m, g = 10 m/s2

\(v = \sqrt{2gh} = \sqrt{2\;\times10\;\times20} = 20\; m\)

∴ The velocity of ball when it reaches the ground is **20 m**