How Does Air Resistance Affect Cyclist Power Output?

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Homework Help Overview

The discussion revolves around the impact of air resistance on a cyclist's power output while traveling at a constant speed of 7.0 m/s on a level road. The original poster presents a problem involving the calculation of the frictional force exerted by air resistance, given a power output of 120 W.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • Participants explore the relationship between power, work, and force, questioning how to derive the frictional force from the given power output. Some participants express uncertainty about missing variables and the implications of constant velocity on acceleration and net force.

Discussion Status

The discussion is active, with participants offering insights into the definitions of power and work, and how they relate to the problem. There is an ongoing exploration of the implications of constant velocity and the forces at play, but no consensus has been reached on a specific approach or solution.

Contextual Notes

Participants note the challenge of missing variables and the need to clarify the definitions and relationships between power, force, and work in the context of the problem.

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Homework Statement


The power of a cyclist moving at a constant speed of 7.0 m/s on a level road is 120 W. What is the magnitude of the frictional force (in N) exerted on her (and the bicycle) by the air?


Homework Equations


P=energy/time KE=1/2mv^2


The Attempt at a Solution


Idk i tried but I'm just missing too many variables.. i attempted and got 4.9N
 
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Power is the rate at which work,W, is done i.e. [itex]P=\frac{d}{dt}(W)[/itex]

W=Fs => (you can take it from here) [Note: constant velocity means constant acceleration which means what about the force and hence you should have a new expression for P]
 
jk5389 said:

Homework Statement


The power of a cyclist moving at a constant speed of 7.0 m/s on a level road is 120 W. What is the magnitude of the frictional force (in N) exerted on her (and the bicycle) by the air?


Homework Equations


P=energy/time

Here are two things to consider. The cyclist is working along to propel the bike, so they must be exerting a force, yet they are moving at constant speed. What is the acceleration of the cyclist and bicycle? What is the net force of the cyclist and bicycle? What must be the power being delivered by the air resistance against the cyclist and bike?

Knowing the power brought to bear by the air, you can take apart the definition of power, which is P = energy/time or work/time. What is the definition of work and how do you calculate it? Work can be written as a product of something, so it can be factored. What would be a way to factor the quotient for power in terms of a quantity you know from the problem and a quantity you want to find?
 
Last edited:
rock.freak667 said:
[Note: constant velocity means constant acceleration...

Erm, but not just any constant -- exactly what acceleration?
 

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