Question

If the force $\overrightarrow{F}=(60\hat{i}+15\hat{j}-3\hat{k})\text{N}$ and velocity $\overrightarrow{v}=(2\hat{i}-4\hat{j}+5\hat{k})\text{m/s}$, then instantaneous power is

• A. $195\text{watt}$
• B. $45\text{watt}$
• C. $75\text{watt}$
• D. $100\text{watt}$

Answer 1

The correct option is B $45\text{watt}$

Power $P=\overrightarrow{F}.\overrightarrow{v}=(60\hat{i}+15\hat{j}-3\hat{k}).(2\hat{i}-4\hat{j}+5\hat{k})$
$P=120-60-15=45\text{watts.}$
Hence, the correct answer is option (b).