A Motorcyclist crossing a stretch of land

[Mioojo]

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

 

[berkeman]

Welcome to the PF.

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?

 

[Mioojo]

Welcome to the PF.

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"

 

[jbriggs444]

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.

 

[haruspex]

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.