Question 50

The terminal velocity of a metallic ball of radius 6 mm in a viscous fluid is 20 cm/s. The terminal velocity of another ball of same material and having radius 3 mm in the same fluid will be ________ cm/ s.

Correct Answer: 5

Terminal velocity $$v_t \propto r^2$$ (from Stokes' law, same material and fluid).

$$\frac{v_2}{v_1} = \frac{r_2^2}{r_1^2} = \frac{9}{36} = \frac{1}{4}$$

$$v_2 = \frac{20}{4} = 5$$ cm/s

The answer is 5 cm/s.

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