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When you ride a bicycle at constant speed, nearly all the
Chapter 11, Problem 64P(choose chapter or problem)
Problem 64P
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 0.45 m2and, because the human body is not aerodynamically shaped, a drag coefficient of 0.90.
a. What is the cyclist’s power output while riding at a steady 7.3 m/s (16 mph)?
b. Metabolic power is the rate at which your body “burns” fuel to power your activities. For many activities, your body is roughly 25% efficient at converting the chemical energy of food into mechanical energy. What is the cyclist’s metabolic power while cycling at 7.3 m/s?
c. The food calorie is equivalent to 4190 J. How many calories does the cyclist burn if he rides over level ground at 7.3 m/s for 1 h?
Questions & Answers
QUESTION:
Problem 64P
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 0.45 m2and, because the human body is not aerodynamically shaped, a drag coefficient of 0.90.
a. What is the cyclist’s power output while riding at a steady 7.3 m/s (16 mph)?
b. Metabolic power is the rate at which your body “burns” fuel to power your activities. For many activities, your body is roughly 25% efficient at converting the chemical energy of food into mechanical energy. What is the cyclist’s metabolic power while cycling at 7.3 m/s?
c. The food calorie is equivalent to 4190 J. How many calories does the cyclist burn if he rides over level ground at 7.3 m/s for 1 h?
ANSWER:
Step 1 of 5
Part (a)
We are going to find the power output of a cyclist who does the work against the air drag.
The area of cross-section of the cyclist \(\mathrm{A}=0.45 \mathrm{~m}^{2}\)
The drag coefficient \(\mathrm{C}=0.90\)
The density of air \(\rho=1.2 \mathrm{~kg} / \mathrm{m}^{3}\)
The speed of the cyclist \(\mathrm{v}=7.3 \mathrm{~m} / \mathrm{s}\)