First slide

Viscosity

Question

Two uniform solid balls of same density and of radii r and 2r are dropped in air and fall vertically downwards. The terminal velocity of the ball with radius r is 1 $cm s^{- 1}$ , then the terminal velocity of the ball of radius 2r will be (neglect buoyant force on the balls.)

Moderate

A

0.5 $cm s^{- 1}$
B

4 $cm s^{- 1}$
C

1 $cm s^{- 1}$
D

2 $cm s^{- 1}$

Solution

At equilibrium
$mg = 6 {πηrv}_{0} or ρ \frac{4 π}{3} r^{3} g = 6 πηrv$
$∴ \frac{v_{r}}{v_{2 r}} = \frac{{(r)}^{2}}{{(2 r)}^{2}} or v_{2 r} = (v_{r}) \times 4 = 4 cm / s$

Get Instant Solutions

When in doubt download our app. Now available Google Play Store- Doubts App

Recieve an sms with download link

Doubts App

OR

SCAN ME

Doubts App

Doubts App