91影视

Power is expressed as the rate of doing work.

$P=\frac{W}{t}$

Here P is the power, W is the work done, t is the work required.

(a)

The word powerful is wrongly used here because the speed with which he does work is usually neglected.

Power is a measure of applying force with speed. A powerful man would have to exert a force that results in displacement with great speed.

Also, the time component is neglected in everyday usage of the word 鈥榩owerful鈥�.

Thus, the statement 鈥淎 strong person is called powerful鈥� has errors.

(b)

When a worker lifts the concrete bag along with a level construction site it results in horizontal displacement.

The vertical force only causes vertical displacement and so it does some work equal to .

Thus, a vertical force cannot cause horizontal displacement, so no work is done when a worker carries a bag of concrete along a level construction site,