Question

A sphere falls from rest into water from a height of 2m. The relative density of the sphere is 0.8. Neglecting the force of impact at the water surface, the depth to which the sphere will sink is

• A. 8m
• B. 4.4m
• C. 3.2m
• D. 4m

Answer 1

The correct option is A 8m

Velocity with which the ball launches the surface $v=\sqrt{2gh}=\sqrt{4g}m{s}^{-1}$
Retardation $a^1=\frac{v\rho h-v\sigma g}{v\rho }=\left(\frac{\rho -\sigma }{\rho }\right)g=\left(\frac{0.8-1}{0.8}\right)g=\frac{-g}{4}$ $(0{)}^2-4g=2\left(\frac{-g}{4}\right)h\Rightarrow h=8m$