Question

A body of mass $0.01kg$ starts to move in a viscous liquid with initial velocity $5m/s$. If drag force is ${10}^{-3}N$ then find time after which velocity will become $\frac{1}{10}m/s$

• A. $49sec$
• B. $100sec$
• C. $149sec$
• D. $200sec$

Answer 1

The correct option is A $49sec$

Initial speed $u=5m/s$

Final speed $v=0.1m/s$

Force $F=0.001N$

Acceleration $a=\frac{-F}{M}=\frac{-0.001}{0.01}=-0.1m/s^2$

Using $v=u+at$

Or $0.1=5+(-0.1)t$

$⟹t=49s$