MCQ
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 indicate the one that represents the velocity $(v)$ of the pebble as a function of time $(t):$
- A
- B
- ✓
- D
✓
Answer
Correct option: C.
In fluids, when the pebble is dropped from the top of a tall cylinder filled with viscous oil, a variable force called viscous force will act which increases with increase in speed. And at equilibrium this velocity becomes constant, that constant velocity is called terminal velocity.
When the pebble is falling through the viscous oil, the viscous force is $\text{F}= 6\pi\eta\text{rv}$ where r is the 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 a straight line. First velocity increases and then becomes constant known as terminal velocity.
When the pebble is falling through the viscous oil, the viscous force is $\text{F}= 6\pi\eta\text{rv}$ where r is the 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 a straight line. First velocity increases and then becomes constant known as terminal velocity.
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