Question

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)`
A.
B.
C.
D.

Answer 1

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