Question

A body of mass 5$kg$ is raised vertically to a height of 10$m$ by a force of 170$N$ . The velocity of the body at this height will be

• A. 37${ms}^{-1}$
• B. 22$m{s}^{-1}$
• C. 15$m{s}^{-1}$
• D. 9.8$m{s}^{-1}$

Answer 1

The correct option is B 22$m{s}^{-1}$

Given,

$m=5kg$

$h=10m$

$F=170N$

Potential energy against gravity,

$P.E=mgh$

$P.E=5\times 10\times 10$

$P.E=500J$

Total work done by the external force,

$W=Fh$

$W=170\times 10$

$W=1700J$

Gain in kinetic energy ,$K.E=W-P.E$

$K.E=1700-500$

$K.E=1200J$

$\frac{1}{2}m{v}^2=1200J$

$\frac{1}{2}\times 5\times v^2=1200J$

$v^2=\frac{2400}{5}=480$

$v=\sqrt{480}m/s$

Velocity, $v=21.90\approx 22m/s$

The correct option is B.