Chapter 9: Q. 4 (page 227)
A horizontal rope with 15 N tension drags a 25 kg box 2.0 m to the left across a horizontal surface. How much work is done by
(a) tension and (b) gravity?
a) Work done by Tension = 30 J
b) Work done by gravity = 0 J
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A elevator accelerates upward at for , starting from rest.
a. How much work does gravity do on the elevator?
b. How much work does the tension in the elevator cable do on the elevator?
c. What is the elevator’s kinetic energy after traveling
The two ropes seen in FIGURE are used to lower a kg piano m from a second-story window to the ground. How much work is done by each of the three forces?
A kg air compressor is dragged up a rough incline from m to m, where theaxis is vertical. How much work does gravity do on the compressor during this displacement?
A horizontal spring with spring constant N/m is attached to a wall. An athlete presses against the free end of the spring, compressing it cm. How hard is the athlete pushing?
When you ride a bicycle at constant speed, nearly all the energy you expend goes into the work you do against the drag force of the air. Model a cyclist as having cross-section area and, because the human body is not aerodynamically shaped, a drag coefficient of .
a. What is the cyclist’s power output while riding at a steady ?
b. Metabolic power is the rate at which your body “burns” fuel to power your activities. For many activities, your body is roughly efficient at converting the chemical energy of food into mechanical energy. What is the cyclist’s metabolic power while cycling at ?
c. The food calorie is equivalent to How many calories does the cyclist burn if he rides over level ground at?
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