A tall cylinder is filled with viscous oil. A round pebble is dropped from the top with zero initial velocity. From the plot shown in figure, indicate the one that represents the velocity `(v)` of the pebble as a function of time `(t)`

Options

A.
B.
C.
D.

Answer

C

Explanation

When the pebble is falling through the viscous oil the viscous force is
`F=6pi eta r v`
Where r is radius of the pebble, v is instantaneous speed. `eta` is coefficient of viscosity.
As the force is variable, hence acceleration is also variable so v-t graph will not be straight line. First velocity increases and then becomes constant known as terminal velocity.