A Motorcyclist crossing a stretch of land

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Homework Help Overview

The discussion revolves around a physics problem involving a motorcyclist crossing a stretch of land, focusing on the forces acting on the motorcyclist and the implications of friction and resistance. The subject area includes dynamics and forces, particularly in the context of motion and energy conservation.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants explore the implications of the motorcyclist coasting without braking, questioning the relevance of kinetic friction versus rolling resistance. Some participants express uncertainty about the completeness of the problem statement and the qualifications of the problem setter.

Discussion Status

The discussion is ongoing, with participants raising questions about the assumptions made in the problem. Some guidance has been offered regarding the role of friction and resistance, but there is no explicit consensus on the interpretation of the problem or its parameters.

Contextual Notes

There is mention of a lack of specific numerical values for rolling resistance, which may affect the interpretation of the problem. Participants also note that the problem setter's qualifications could influence the understanding of the concepts involved.

Mioojo
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Homework Statement
A motorcyclist at a constant speed of 20 km/h with the motorcycle motor off. He tries to cross a 15 m Stretch of land with kinetic friction coefficient of 0.7 . Can he?
Relevant Equations
None given
TA = Ec

0,7*m*g*d = (m*v² /2)


1,4*g*d = (400/12,96)


14*d = (400/12,96)


d = 2,2 m

No
 
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Welcome to the PF. :smile:

If the motorcyclist is free-wheeling (no braking force), why wouln't they just keep coasting at the same speed? Is there more to the problem statement?
 
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berkeman said:
Welcome to the PF. :smile:

If the motorcyclist is free-wheeling (no braking force), why wouln't they just keep coasting at the same speed? Is there more to the problem statement?
Thx.

The problem statement has all the information that was given to me. And I know that the answer to the problem is "No"
 
Mioojo said:
The problem statement has all the information that was given to me. And I know that the answer to the problem is "No"
As @berkeman hints, the correct answer is "Yes".

The coefficient of kinetic friction only comes into play if the brakes are applied hard enough that the tires skid. Most motorcyclists avoid applying the brakes when trying to coast and definitely try to avoid locking up both front and back tires at the same time.
 
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This is one of those tricky questions where you have to guess the expertise of the problem setter.
If the problem setter is properly qualified to be setting physics questions then, as others have noted, the kinetic friction information is irrelevant. All that need slow the motorcyclist is rolling resistance, which is typically a much lower value. But since you are not told a number for that, the correct answer is "not enough info".
However, if the problem setter is not so qualified, it may be a blunder, and the setter does not understand the difference between kinetic friction and rolling resistance.
 
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