The lever on an old voting machine is jammed. An election official attempts to u

Question

The lever on an old voting machine is jammed. An election official attempts to un-jam the lever by exerting a force F from the end of the lever towards the point at which the lever pivots, a distance r away. What is the torque exerted on the lever? A. 0 B. rF C. rF/2 D. Cannot be determined While scratching records, a DJ exerts a constant force F tangential to the direction of the record's rotation at radius r in order to slow the record's angular velocity from omega to omega/2. If the DJ exerts this constant force while the record turns through angle theta, what is theta? Assume the record's moment of inertia is I. A. 3 I omega^2/8r F B. 3 I omega^2/4r F C. I omega^2/2r F D. 3 I omega^2/2r F Pulling with a force F along the length of an aluminum rod with the other end fixed to a wall causes rod increase in length by 1%. If the force was instead F/2, what the would have happened to the rod? A. the rod would decrease in length by 0.5% B. the rod would decrease in length by 1% C. the rod would increase in length by 0.5% D. the rod would increase in length by 2%

Explanation / Answer

8) Torque = force x distance of line of force from pivot
   = Fr

9) w2 = Wo2 + 2 (alpha theta)
   alpha = torque / moment of inertia = Fr/I
   Hence (w/2)2 = w2 - 2 (Fr/I) theta ( alpha and theta are in opposite dircetion)
theta = 3 I w2 / 8 Fr

10) F = YA ( delta L / L)
   Hence force is proportional to delta L/L
   With force becoming half percentage increase in length is half, that is 1/2 percent

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