Question

A weight lifter picks up a barbell and

Answer 1

Answer:

From highest to lowest: $W_1>W_2>W_3$

Explanation:

The work done by a force is given by

$W=Fd cos \theta$

where:

F is the force applied on the object

d is the displacement of the object

$\theta$ is the angle between the direction of the force and of the displacement

In case 1), the barbell is lifted upward. This means that:

- the force applied is upward

- the displacement of the object is upward

This means that $0$, so the work done is positive: $W_1>0$

In case 2), the barbell is held stationary: this means that the displacement is zero,

$d=0$

And therefore, this means that the work done is also zero:

$W_2=0$

In case 3), the barbell is put down slowly, without dropping it. This means that:

- The force applied is still upward (in fact, the force applied must be upward in order to overcome the force of gravity downward, and avoid the barbell to fall down)

- The displacement of the barbell is downward

This means that $90^{\circ}$, so $cos \theta$, and therefore the work done is negative:

$W_3$

So the ranking from greatest to smallest work is

$W_1>W_2>W_3$