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# Lecture7a1(1)

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### Lecture7a1(1)

1. 1. Today: Virtual Work continued Book: Chapter 11.1-11.3 + hand-out on Blackboard
2. 2. The principle of virtual work (body in two dimensions) A particle is in equilibrium when for any virtuall displacement and/or rotation, the virtual work is equal to zero. 0i i i ix x y y i iW u F u F M        
3. 3. Mechanisms Small angle approach no longer valid!
4. 4. Determine the force N exerted on the log by each jaw of the fireplace tongs shown
5. 5. Determine the couple M required to maintain equilibrium at an angle θ. Each of the two uniform bars has mass m and length l.
6. 6. Determine the torque M on the activating lever of the dump truck necessary to balance the load of mass m with centre of mass at G when the dump angle is θ. The polygon ABDC is a parallelogram.
7. 7. The height of the platform with mass m is determined by the hydraulic pistons AB and AC which rotate about point A. Determine the compressive force P in each of the two pistons for a specific angle .
8. 8. Next time: Exam October 27, 2006