A copper ball of radius `r` travels with a uniform speed v in a viscous fluid if the ball is changed with another ball of radius 2r then new uniform speed will be

Options

A. 4V
B. 2V
C. `V/2`
D. V

Answer

A

Explanation

Due to uniform speed `F_"net"` on it is zero which is
`upsilon T prop r^2`
`(upsilon T_2)/(upsilon T_1)=((2r)^2)/r^2`
`upsilonT_2=4v`
Now if redius is doubled speed will be four times.