Rigid-Body Work - Example Problem 8.2-3

 

A 100-lb block is suspended from an inextensible cable, which is wrapped around the outer radius (r = 1.3 ft) of a flywheel. The flywheel rotates on a shaft supported by bearings. The bearings are poorly lubricated and apply a M_f = 30 lb-ft frictional moment to the flywheel. If the block drops h = 3 ft, determine the work done by the weight and the friction.

 

 

Given:

• W_B = 100 lb
• r = 1.3 ft
• M_f = 30 lb-ft
• h = 3 ft

 

Find:

• U_W
• U_M

 

Video solution:

 

The following video walks you through the solution to this problem. It is suggested that you try solving the problem first and then, if you have difficulties with the solution, watch the video for help.

 

 

Interactive solution:

 

Determine the work done by the body's weight force. Which equation is the easiest to use for this situation?

 

U = ∫F ⋅ dr
U = Fd
U = Mθ