Question

A ball of mass $1\text{kg}$ is falling under gravity in a viscous medium. The drag force on it is given by $0.5u$, where $u$ is the instantaneous speed. If upthrust force on it is $5\text{N}$, then terminal speed (in $\text{m/s}$) is
​​​​​​​(take $g=10{\text{ms}}^{-2}$)

Answer 1

FBD of ball according to question:


Net force on ball at any instant,
$F=10-0.5u-5$
We know that, when ball reaches terminal speed, the speed is constant and net force on it is zero.
$\therefore 10-0.5u-5=0$
$\Rightarrow u=10\text{m/s}$
The terminal speed of the ball is $10\text{m/s}$