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

Options

A. `0.5cms^-1`
B. `4cms^-1`
C. `1cms^-1`
D. `2cms^-1`

Answer

B

Explanation

At equilibrium
`mg=6pietarv_0` or `rho(4pi)/(3)g=6pietarv`
`(v_r)/(v_(2r))=((r )^2)/((2r)^2)` or `v_2r=(v_r)xx4=4(cm)/(s)`