Homework Help: physics

Posted by Anonymous on Tuesday, December 11, 2012 at 11:02pm.

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

physics - Elena, Wednesday, December 12, 2012 at 7:15am
μ=0.14, s=30
m=160 kg

x: m•a= m•g•sinα - F(fr),
y: 0= - m•g•cosα +N.

F(fr)=μ•N= μ• m•g•cosα
m•a= m•g•sinα - μ• m•g•cosα
a= g(sinα - μ•cosα)
v=sqrt(2as)
t=v/a

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