Homework Help: physics

Posted by Sara on Monday, March 14, 2011 at 11:02pm.

A dock worker loading crates on a ship finds
that a 25 kg crate, initially at rest on a hori-
zontal surface, requires a 90 N horizontal force
to set it in motion. However, after the crate
is in motion, a horizontal force of 51 N is
required to keep it moving with a constant
speed.
The acceleration of gravity is 9.8 m/s2 .
Find the coefficient of static friction be-
tween crate and floor.

physics - drwls, Tuesday, March 15, 2011 at 7:39am
90 N = M * g * mu_s

Solve for the static friction coefficient, mu_s

M = 25 kg
g = 9.8 m/s^2

The 51 N force can be used to compute the kinetic friction coefficient, but they didn't ask for that.

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