# Coefficient of Friction Needed?

1. May 20, 2009

### haganjp

1. The problem statement, all variables and given/known data
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?

2. Relevant 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

3. 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

2. May 20, 2009

### Sourabh N

Yes, seems information given in question is insufficient.

3. May 20, 2009

### fatra2

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, $$\mu = 0.05$$ is not a very big coefficient, which could definitely be right.

4. May 20, 2009

### diazona

For the Regents exam... somehow I'm not too surprised :-/