A paddle wheel (Fig.) requires a torque of 20 ft-lbf to rotate it at 100 rpm. If it rotates for 20 s, calculate the net work done by the air if the frictionless piston raises 2 ft during this time.
Text Solution
Verified by ExpertsCHECK THE SOLUTION.
Sol. The work input by the paddle wheel is
W = – T ω Δ t = (–20 ft-lbf) 
(20 s) = – 4190 ft-lbf
The negative sign accounts for work being done on the system, the air. The work needed to raise the piston requires that the pressure be known. It is found as follows:
PA = P atm A + W P 
= (14.7) 
+ 500
∴ P = 32.4 psia
The work done by the air to raise the piston is then
W = (F) = (P) = (32.4) 
(2) = 1830 ft-lbf
and the net work is W net = 1830 – 4190 = – 2360 ft-lbf.
Prepare Smarter with CGP Edu
Get practice questions, solutions, and test series in one place.
Write a Review
Share your experience with this question and solution.
Commentary
Send your comment, doubt, correction, or feedback to admin.
Similar Questions
Explore conceptually related problems