【Daily Question】Theoretical Foundation 2020.03.27
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Multiple-choice question: As shown in the figure, the torque diagram of the circular shaft is ( ). Answer: D Hint: Extra rewards will be given to those who can explain the solution process; the answer can be seen there!
Choose D. First, consider the overall balance; assuming that the reaction couple m at the left end rotates from the outside inward on the outer surface, we have ∑M=0, which means m – 1 – 6 – 2 + 5 = 0. Therefore, m = 4 kN·m. The torque for each segment is then calculated using the direct method; the torques from left to right are 4 kN·m, 3 kN·m, -3 kN·m, and -5 kN·m respectively. The change in torque at the sections on either side of a concentrated couple equals the magnitude of the couple’s moment. Only Diagram D clearly conforms to these rules for the torque diagram.