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# Chapter 10 Problems - page 10 / 19

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a spool of radius r, forming part of a turntable supporting the object. The turntable can rotate without friction.  When the counterweight is released from rest, it descends through a distance h, acquiring a speed v. Show that the moment of inertia I of the rotating apparatus (including the turntable) is mr2(2gh/v2 – 1).

Figure P10.47

48.A horizontal 800-N merry-go-round is a solid disk of radius 1.50 m, started from rest by a constant horizontal force of 50.0 N applied tangentially to the edge of the disk. Find the kinetic energy of the solid disk after 3.00 s.

49.(a) A uniform solid disk of radius R and mass M is free to rotate on a frictionless pivot through a point on its rim (Fig. P10.49). If the disk is released from rest in the position shown by the blue circle, what is the speed of its center of mass when the disk reaches the position indicated by the dashed circle? (b) What is the speed of the lowest point on the disk in the dashed position? (c) What If? Repeat part (a) using a uniform hoop.

Figure P10.49

50.The head of a grass string trimmer has 100 g of cord wound in a light cylindrical spool with inside diameter

3.00 cm and outside diameter 18.0 cm, as in Figure P10.50. The cord has a linear density of 10.0 g/m. A single strand of the cord extends 16.0 cm from the outer edge of the spool.  (a) When switched on, the trimmer speeds up from 0 to 2 500 rev/min in

0.215 s.  (a) What average power is delivered to the head by the trimmer motor while it is accelerating?  (b) When the trimmer is cutting grass, it spins at

2 000 rev/min and the grass exerts an average tangential force of 7.65 N on the outer end of the cord, which is still at a radial distance of 16.0 cm from the outer edge of the spool.  What is the power delivered to the head under load?

Figure P10.50

Section 10.9 Rolling Motion of a Rigid Object

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