# Problem With Maximum Acceleration up Hill

Problem With Maximum Acceleration up Hill!!

## Homework Statement

cross-country skier is going up a slope at angle 5º to the horizontal. She is skating so only her skis provide the propulsion (i.e. she does not push with her ski poles). The static and kinetic friction coefficients for this situation are μs = 0.12, μk = 0.07 respectively.

Find the magnitude of her maximum possible uphill acceleration?

Fnet=MA

## The Attempt at a Solution

So Far:

Fnet(x)= F(static) - F(kinetic) - Fg = ma

Fnet(x) = (0.12 x m x 9.8cos85) - (0.07 x m x 9.8cos85) - (9.8cos85 x m) = ma

Divide by m you get:

Fnet(x) = (0.12 x 9.8cos85) - (0.07 x 9.8cos85) - 9.8cos85 = a

Therefore a= - 0.81m/s^2

But this gives me a negative accelleration, Where did I go wrong? as it asks for the Max acceleration up the hill and that acceleration would point down hill.

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ideasrule
Homework Helper

How can she possibly accelerate uphill?

She uses her skis to push against the ground which propells her forward through static friction.

ideasrule
Homework Helper

I thought the question said "i.e. she does not push with her ski poles".

she DOES NOT use her poles, but she DOES use her skis - the same way people ice skate

PhanthomJay
Homework Helper
Gold Member

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