14. Torque & Rotational Dynamics

Torque Due to Weight

Multiple Choice
Two kids play on a seesaw that has mass 20 kg, length 3 m, and its fulcrum at its mid-point. The seesaw is originally horizontal, when the kids sit at the edge of opposite ends (m,_LEFT = 25 kg, m,_RIGHT = 30 kg). Calculate the Net Torque from the 3 weights acting on the seesaw, immediately after the kids sit (simultaneously) on their respective places.
Multiple Choice
A guy standing straight up stretches out his arm horizontally while holding a 60 lb (27.2 kg) barbell. His arm is 64 cm long and weighs 45 N. Calculate the Net Torque that the barbell and the weight of his arm produce about his shoulder. You may assume that his arm has uniform mass distribution.
Multiple Choice
Consider the diagram below of a typical human arm lifting a weight in a motion known as a 'curl.' Peak human training of such an arm can result in record lifts of 110 kg. Increasing a lift by a single kilogram in competition can make all the difference. Now, suppose a particular human had a bicep tendon that attached just 5.0 mm farther from the elbow joint than usual. Given the same bicep strength as other peak-condition athletes, what weight could this person curl (lift in this way)?
Open Question
A 4.0-m-long, 500 kg steel beam extends horizontally from the point where it has been bolted to the framework of a new building under construction. A 70 kg construction worker stands at the far end of the beam. What is the magnitude of the torque about the bolt due to the worker and the weight of the beam?
Open Question
(I) What is the mass of the diver in Fig. 12–52 if she exerts a torque of 1800 m · N on the board, relative to the left (A) support post?
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