An elevator held by a single cable is ascending but slowing down. Which of the f

Question

An elevator held by a single cable is ascending but slowing down. Which of the following is true about the work done by the tension in the cable and work done by gravity?

a) The work done by tension is positive while the work done by gravity is negative.

b) Both tension and gravity do positive work.

c) The work done by tension is negative while the work done by gravity is positive

d) Both tension and gravity do negative work.

e) The work done by tesion is equal to the work done by gravity.

(Please answer with details of explanation, included formula can be applied if necessary).

Explanation / Answer

Work done by a force is F.S = FS cos theta
where F is magnitude of force, S is magnitude of displacement and theta is the angle between force and displacement vectors. If theta is less than 90 deg., cos theta as well as work of force is +ve. For theta between 90 and 180 deg. , cos(theta) as well as work done by force is -ve.
As Lift is ascending , it's displacement is upward. Force of tension is upward while force of grvity is downward.
Angle between tension and displacement is zero and cos(0) = +1. Hence work doe by tension is +ve.
Angle between displacement and force of gravity is 180, cos (180) = -1, hence work done by gravity is -ve.
Option a is correct

Related Questions

Navigate

• Browse (All)
• Browse A
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.