Calculating Work Done by Friction in a Downhill Race: Conservation of Motion

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Homework Help Overview

The problem involves calculating the work done by friction for a boy in a wheelchair racing downhill. The scenario includes variables such as mass, height of the slope, and speeds at different points, with a focus on the forces acting against motion.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants discuss the general expression for work and the specific contributions of different forces, including gravity and friction. There is uncertainty about how to set up the equations correctly and what constitutes the outside forces.

Discussion Status

Some participants have provided guidance on identifying the work done by gravity and have pointed out the need to clarify the height used in calculations. There is an ongoing exploration of the relationship between the various forces and the work done.

Contextual Notes

There is mention of a constant frictional force and the need to distinguish between different types of work in the context of the problem. Participants express frustration over the complexity of the setup and seek clarification on the definitions involved.

Chuck 86
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Homework Statement


boy in a wheelchair (total mass, 48.7 kg) wins a race with a skateboarder. He has a speed of 1.23 m/s at the crest of a slope 2.37 m high and 14.0 m long. At the bottom of the slope, his speed is 6.27 m/s. If air resistance and rolling resistance can be modeled as a constant frictional force of 41.8 N, calculate the work he did in pushing forward on his wheels during the downhill ride.


Homework Equations


Ei-Ef=Wfriction+Woutside forces

1/2mv^2, mgh

The Attempt at a Solution


cant seem to set this up right. don't know the equations for the 2 work
 
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Can't you think of a general expression for work that you could use here?
 
Not of the outside forces
 
that would be cool to get some help instead of pointing out that I am not smart, that's why I am asking for help
 
What are the outside forces?

In particular, what is the work done by gravity?
 
MgH=(48.7)(9.8)(14)
 
OK but H=2.37 m here, not 14m.

Now you just need to calculate the work done by friction.
 

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