A free body around pulley A shows that the torque on shaft AB is - 400 lb-in clockwise (cw); a second free body around pulleys A & B shows that the torque in BC is - 400 + 1200 or 800 lb-in; a third around pulleys A, B, & C shows that the torque in CD is - 400 + 1200 + 500 or 1300 lb-in. (I am taking counterclockwise as positive.)
The formulas to be used are:
Since the same calculations must be done
three times, it's easier to express the results in a table:
| shaft | torque (lb-in) | c (in) | J (in4) | t (ksi) |
| AB | - 400 | 0.300 | 1.272 x 10-2 | 9.43 |
| BC | 800 | 0.375 | 3.106 x 10-2 | 9.66 |
| CD | 1300 | 0.450 | 6.44 x 10-2 | 9.08 |
The maximum shearing stress occurs in shaft BC.