Unformatted text preview: t and (b) the force exerted by the seat on
the child at the lowest point. (Neglect the mass of the
seat.) x B
A Figure P6.12
13. Consider a conical pendulum with an 80.0kg bob on a
10.0m wire making an angle of
5.00° with the vertical (Fig. P6.13). Determine (a) the horizontal and vertical components of the force exerted by the wire on the
pendulum and (b) the radial acceleration of the bob. θ WEB 19. A pail of water is rotated in a vertical circle of radius
1.00 m. What must be the minimum speed of the pail at
the top of the circle if no water is to spill out?
20. A 0.400kg object is swung in a vertical circular path on
a string 0.500 m long. If its speed is 4.00 m/s at the top
of the circle, what is the tension in the string there?
21. A rollercoaster car has a mass of 500 kg when fully
loaded with passengers (Fig. P6.21). (a) If the car has a
speed of 20.0 m/s at point A, what is the force exerted
by the track on the car at this point? (b) What is the
maximum speed the car can have at B and still remain
on the track? B 15.0 m Figure P6.13
Section 6.2 10.0 m
A Nonuniform Circular Motion 14. A car traveling on a straight road at 9.00 m/s goes over
a hump in the road. The hump may be regarded as an
arc of a circle of radius 11.0 m. (a) What is the apparent
weight of a 600N woman in the car as she rides over the Figure P6.21 175 Problems
22. A roller coaster at the Six Flags Great America amusement park in Gurnee, Illinois, incorporates some of the
latest design technology and some basic physics. Each
vertical loop, instead of being circular, is shaped like a
teardrop (Fig. P6.22). The cars ride on the inside of the
loop at the top, and the speeds are high enough to ensure that the cars remain on the track. The biggest loop
is 40.0 m high, with a maximum speed of 31.0 m/s
(nearly 70 mi/h) at the bottom. Suppose the speed at
the top is 13.0 m/s and the corresponding centripetal
acceleration is 2g. (a) What is the radius of the arc of
the teardrop at the top? (b) If the total mass of the cars
plus people is M, what force does the rail exert on this
total mass at the top? (c) Suppose the roller coaster had
a loop of radius 20.0 m. If the cars have the same speed,
13.0 m/s at the top, what is the centripetal acceleration
at the top? Comment on the normal force at the top in
this situation. 24. A 5.00kg mass attached to a spring scale rests on a frictionless, horizontal surface as in Figure P6.24. The
spring scale, attached to the front end of a boxcar, reads
18.0 N when the car is in motion. (a) If the spring scale
reads zero when the car is at rest, determine the acceleration of the car. (b) What will the spring scale read if
the car moves with constant velocity? (c) Describe the
forces acting on the mass as observed by someone in
the car and by someone at rest outside the car. 5.00 kg Figure P6.24 Figure P6.22 (Frank Cezus/FPG International) (Optional) Section 6.3 Motion in Accelerated Frames 23. A merrygoround makes one complete revolution in
12.0 s....
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 Fall '13
 Circular Motion, Force, other applications

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