A small girl and boy take a sled up to the top of a snow covered slope which is

Question

A small girl and boy take a sled up to the top of a snow covered slope which is inclined 30 degrees above the horizontal. The girl, boy and the sled have a mass of 160 kg. The coefficient of static friction is 0.28 and the coefficient of kinetic friction is 0.14 between the sled and the snow. They hop on, push off and slide down the 30 meter long incline. a. How fast are they going at the bottom? b. How long does it take them to go the 30 meters?

Explanation / Answer

mgsin30 = 800 ; 0.28mgcos30 = 387.979 ; so sled is moving ; acceleration = gsin30 - 0.14gcos30 = 3.78 = 3.8 m/s^2 velocity at bottom : v^2 =u^2 +2.a.l => v=sq. root(2.a.l) = 15.09 m/s time taken : v=u+at => t = v/a = 15.09/3.83.97 seconds.

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