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Coefficient of Friction Needed?

  • Thread starter haganjp
  • Start date
  • #1
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Homework Statement


I was reviewing some questions from the NYS Regents Physics exam and came across this question, which I could not answer. Here's the question ...

An 80-kg skier slides on waxed skis along a horizontal surface of snow at constant velocity while pushing with his poles. What is the horizontal component of the force pushing him forward?

Homework Equations



In the horiztonal direction ...

Sum of Forces = mass x acceleration = 0 (constant velocity, therefore a=0)
Sum of Forces = Applied Force - Friction Force = 0

Applied Force = Friction Force
where, Friction Force = Coefficent of Friction x Normal Force

Normal Force = m x g = 80kg * 9.81 m/s^2 = 784.8 N


The Attempt at a Solution



It seems I cannot determine a solution unless I know what the coefficient of friction is (which was not given in the problem statement). Am I missing something here?

It seems that it is implied that the surface is frictionless, in which case there is no need to apply a force to keep moving at a constant velocity, yet the answer key states that 40N of force are required. If this is indeed the answer, then a coefficient of friction of 0.05 is implied.

Thanks,

Jim
 

Answers and Replies

  • #2
631
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Yes, seems information given in question is insufficient.
 
  • #3
472
0
Hi there,

From the information you gave in this problem, there is really an information missing. In my understanding also, the idea of the wax on the skis reduces the friction coefficient to a minimum.

Then again, [tex]\mu = 0.05[/tex] is not a very big coefficient, which could definitely be right.
 
  • #4
diazona
Homework Helper
2,175
6
For the Regents exam... somehow I'm not too surprised :-/
 

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