Question

A truck of mass $500kg$ moving with constant speed $10m/s$. If sand is dropped into the truck at the constant rate $10kg/min$., the force required to maintain the motion with constant velocity is:

• A. $\frac{5}{3}N$
• B. $\frac{5}{4}N$
• C. $\frac{7}{5}N$
• D. $\frac{3}{2}N$

Answer 1

The correct option is A $\frac{5}{3}N$

$F=u\frac{dm}{dt}+m\frac{du}{dt}=u\frac{dm}{dt}$ since $u$ is constant.
$\therefore F=10m/s\times 10kg/min=10\times \frac{10}{60}kgm/s^2=\frac{5}{3}N$