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 ?
a. The output power of the cyclist is .
b. The metabolic power of the cyclist is .
c. The amount of energy burnt by the cyclist is .
The output power of the cyclist due to drag force is
The equation of the drag force is,
Here, is the drag coefficient, is density, is cross section area.
The output power of the cyclist is
The efficiency of body converting chemical energy into mechanical energy is
The metabolic power of the cyclist is
A weather rocket generates a thrust of The rocket, pointing upward, is clamped to the top of a vertical spring. The bottom of the spring, whose spring constant is , is anchored to the ground.
a. Initially, before the engine is ignited, the rocket sits at rest on top of the spring. How much is the spring compressed?
b. After the engine is ignited, what is the rocket’s speed when the spring has stretched
An kg crate is pulled m up a incline by a rope angled above the incline. The tension in the rope is N, and the crate’s coefficient of kinetic friction on the incline is .
a. How much work is done by tension, by gravity, and by the normal force?
b. What is the increase in thermal energy of the crate and incline?
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