Question

A 500 lb steel beam is lifted up by a crane to a height of 100 ft and is held there.

Answer 1

A. How much work is being done to hold the beam in place?

Work is the product of Force and Displacement. Since there is no Displacement involved in just holding the beam in place, hence the work is zero.

 

B. How much work was done to lift the beam?

In this case, force is simply equal to weight or mass times gravity. Hence the work is:

Work = weight * displacement

Work = 500 lbf * 100 ft

Work = 50,000 lbf * ft

 

C. How much work would it take if the steel beam were raised from 100 ft to 200ft?

The displacement is still 100 ft since 200 – 100 = 100 ft, hence the work done is still similar in B which is:

Work = 50,000 lbf * ft