Answer:
3. Wg is positive and WT is negative.
Explanation:
The work done by a force is given by:
[tex]W=Fdcos \theta[/tex]
where
F is the force
d is the displacement of the object
[tex]\theta[/tex] is the angle between the directions of F and d
This means that:
- When force and displacement are parallel, [tex]\theta=0, cos \theta=+1[/tex], so the work done is positive
- When force and displacement are anti-parallel, [tex]\theta=180^{\circ}, cos \theta=-1[/tex], so the work done is negative
In this case, the crane is moving downward. The force of gravity is also downward, while the tension in the cable is upward. so we have:
- Wg is positive, because gravity is parallel to the displacement
- Wt is negative, because the tension is opposite to the displacement
