Your friend has entered a skiing competition where the purpose of the competitio

Question

Your friend has entered a skiing competition where the purpose of the competition is to be the slowest person down an 18º slope without stopping. Having just finished taking physics, your friend asks you for help in applying the best wax compound to her skies to provide the required friction. Blue wax has a coefficient of kinetic friction of 0.30, green is 0.25, yellow is 0.20, and red is 0.15. Wax that is too slippery will cause too large an acceleration while wax that is too sticky will cause her to stop and therefore be disqualified. You measure a strong horizontal headwind of 30 N that is applied to your friend as she skis, regardless of her speed, and you record the mass of your friend to be 55 kg. Which wax do you choose?

Explanation / Answer

Net force down the slope=>0 to keep her in motion. So, mg*sin18°- 30*cos18°-umg*cos18°>=0 { where u= coefficient of friction }

166.73- 28.53-513.14u>=0

So, 0.27>=u

So, for 0.25 you choose green wax

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