Question

A crate of potatoes of mass 12.0 kg is on a ramp with angle of incline 30° to the horizontal. The coefficients of friction are μs = 0.69 and μk = 0.43. Find the frictional force (magnitude and direction) on the crate if the crate is sliding down the ramp.

Answer 1

First, we'll find the force vector of the crate parallel to the slope on which it rests.

Force = (mass)(gravity)cos(30deg)

N = (12.0kg)(9.8m/s^2)cos(30deg)

N = 101.84

Becasue your crate is sliding down the ramp, your direction will be up the ramp.

ìs= Static Friction
ìk= Kinetic Friction

Because you said the crate is moving, we will only be using ìk. (so this means that ìs is negligible information in this problem).

So, (101.84N)(uk) = (101.84)(0.43) = 43.79N

So, the answer to (a) magnitude is 43.79N and (b) the direction is up the ramp.

Hope this helps!