Question

A block of mass $m=3\text{kg}$ is pulled by a force $F=50\text{N}$ upwards through $2\text{m}$ height in vertical direction. It takes $8\text{seconds}$ to lift the mass. Find the average power delivered by the force.

• A. $12.5\text{W}$
• B. $25\text{W}$
• C. $20\text{W}$
• D. $50\text{W}$

Answer 1

The correct option is A $12.5\text{W}$

Work done by the applied force $W_F=Fh\cos \theta$, where $h$ is height.
Here, $\theta =0^{\circ }$, because displacement is in the same direction of force applied.
$\Rightarrow W_F=Fh\cos 0^{\circ }=Fh=50\times 2$
$\Rightarrow W_F=100\text{J}$

Average Power $=\frac{\text{Total work done by the force}}{\text{Total time taken}}$
$=\frac{100}{8}=12.5\text{W}$