73. At which point on the graph is the acceleration of the mass zero? a.A c.C b.B d.D

74. At which point on the graph is the velocity of the mass zero? a.A c.C b.B d.D

75. At which point on the graph is the net force on the mass at a maximum? a.A c.C b.B d.D

76. On the graph, mark the amplitude.

77. A child swings back and forth on a playground swing. If the child stands rather than sits, the time for a to-and-fro swing is __________. Explain.

78. An astronaut lands on an unknown planet and must determine the value of the gravitational acceleration g using a simple pendulum at the end of an arm that is 0.500 m long. The astronaut counts exactly 47 full swings in 1.00 min. What is the value of g?

79. The frequency of the second hand on a clock is __________.

80. A simple pendulum has a string that is 20.0 cm long with a 100.0-g mass suspended from the end. Pulling the mass 2.0 cm to one side and releasing it starts the pendulum in motion. a.What is the amplitude of this pendulum?

b.What is the period of this pendulum?

c.If the string is lengthened to 50.0 cm, what happens to the period? (Be very specific.) d.If the mass is increased to 500.0 g, what happens to the period? e.If the mass is pulled 4.5 cm to one side and released, what happens to the period?

81. Part a of the figure below shows a pulse traveling at a speed of 1.0 m/s in a coil spring to which a second spring is attached at point A. Part b of the figure shows the springs a short time later.

What is the amplitude of the incident pulse?

82. A spring stretches by 24 cm when a block is suspended from its end. The elastic potential energy stored in the spring is 5.4 J when it is stretched this far. Find the weight of the block.

83. Spring A with a spring constant of 279 N/m is stretched by a distance of 18 cm when a block is suspended from its end. An object is suspended from another spring B with a spring constant of 145 N/m. If the elastic potential energy in both the springs is the same, how far does spring B stretch?

84. Hiroshi is generating waves on a rope by flipping the rope up and down. Each motion up or down lasts 0.20 s. The distance from a crest to a trough is 0.40 m. a.What is the amplitude of the wave?

b.What is the frequency of the waves?

85. A lifeguard on a beach observes that waves have a speed of 2.6 m/s and a distance of 2.5 m between wave crests. What is the period of the wave motion?

86. A water wave travels a distance of 15 m in 2 min. When this wave passes a point where a cork is floating in the water, it causes the cork to move up and down 12 times in 15 s. a. What is the period of this water wave?

b. What is the wavelength of this water wave?

87. Waves in a lake are 2 m in length and pass an anchored boat 0.5 s apart. What is the speed of the waves?

88. A pulse with an amplitude of 0.53 m travels to the right along a rope. Another pulse, with an amplitude of –0.24 m, travels to the left along the same rope. The two pulses approach each other. What is the amplitude of the rope at the point where the midpoints of the pulses pass each other?

89. Zeke plucks a C on his guitar string, which vibrates with a fundamental frequency of 261 Hz. The wave travels down the string with a speed of 400 m/s. What is the length of the guitar string?

90. On a harp, long strings produce ___________ notes and short strings...