Cyclist coasting down a hill cons. of energy

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A bicyclist coasts down a 7.0° hill at a steady speed of 5.0 m/s, with a total mass of 75 kg. To determine the power output required to climb the hill at the same speed, the cyclist's energy considerations include kinetic and gravitational potential energy. The calculations suggest that friction must be accounted for, as coasting at a constant speed implies opposing forces are present. The final power output calculated was 448W, but the presence of friction needs to be factored into the overall analysis. Understanding these forces is crucial for accurately determining the cyclist's power requirements.
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Homework Statement


A bicyclist coasts down a 7.0° hill at a steady speed of 5.0m/s. Assuming a total mass of 75kg (bicycle plus rider), what must be the cyclist's power output to climb the same hill at the same speed?


Homework Equations


EK=1/2 mv2
EG=mgh
P=W/T


The Attempt at a Solution


I tried the question and this is what I got but I'm answer if this is right... not sure if there's a Force of friction though because I read the question and assumed there isn't any force of friction... but I'm unsure... :rolleyes:

P=W/T
P=-WGΔdcos180°/T
P=-WGvcos180°
P=-mgsin7.0°(5.0)cos180°
P=-(75)(9.8)sin7.0°(5.0)cos180°
P=448W
 
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Well if the cyclist goes down the hill with constant speed, then there must be some kind of force that's stopping him from accelerating, so you should account for it accordingly.
 
hi totallyclone! :smile:
totallyclone said:
A bicyclist coasts down a 7.0° hill at a steady speed of 5.0m/s. Assuming a total mass of 75kg (bicycle plus rider), what must be the cyclist's power output to climb the same hill at the same speed?
…
not sure if there's a Force of friction …

he couldn't coast (at a steady speed) if there wasn't friction, could he? :wink:
 
tiny-tim said:
hi totallyclone! :smile:


he couldn't coast (at a steady speed) if there wasn't friction, could he? :wink:

so...THERE'S FRICTION!?
 
yup! :smile:
 
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