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# Chapter 10 Problems - page 12 / 19

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consists of three thin rods, each 10.0 cm long.  The rods diverge from a central hub, separated from each other by 120°, and all turn in the same plane.  A ball is attached to the end of each rod.  Each ball has cross-sectional area 4.00 cm2 and is so shaped that it has a drag coefficient of 0.600.  Calculate the power input required to spin the beater at 1 000 rev/min (a) in air and (b) in water.

59.A 4.00-m length of light nylon cord is wound around a uniform cylindrical spool of radius 0.500 m and mass 1.00 kg. The spool is mounted on a frictionless axle and is initially at rest. The cord is pulled from the spool with a constant acceleration of magnitude 2.50 m/s2. (a) How much work has been done on the spool when it reaches an angular speed of 8.00 rad/s? (b) Assuming there is enough cord on the spool, how long does it take the spool to reach this angular speed? (c) Is there enough cord on the spool?

60. A videotape cassette contains two spools, each of radius rs, on which the tape is wound.  As the tape unwinds from the first spool, it winds around the second spool.  The tape moves at constant linear speed v past the heads between the spools.  When all the tape is on the first spool, the tape has an outer radius rt.  Let r represent the outer radius of the tape on the first spool at any instant while the tape is being played.  (a) Show that at any instant the angular speeds of the two spools are

1 = v/r     and 2 = v/( rs2 + rt2 r2 )1/2

(b)  Show that these expressions predict the correct maximum and minimum values for the angular speeds of the two spools.

61. A long uniform rod of length L and mass M is pivoted about a horizontal, frictionless pin through one end. The rod is

released from rest in a vertical position, as shown in Figure P10.61.  At the instant the rod is horizontal, find (a) its angular speed, (b) the magnitude of its angular acceleration, (c) the x and y components of the acceleration of its center of mass, and (d) the components of the reaction force at the pivot.

Figure P10.61

62.A shaft is turning at 65.0 rad/s at time t = 0.  Thereafter, its angular acceleration is given by