A dock worker loading crates on a ship finds
that a 24 kg crate, initially at rest on a hori-
zontal surface, requires a 88 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.
Find the coefficient of kinetic friction.
that a 24 kg crate, initially at rest on a hori-
zontal surface, requires a 88 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.
Find the coefficient of kinetic friction.
-
to get the crate moving, the applied force must just exceed the frictional force;
the frictional force = us N where us is the coeff of static friction and N is the normal force
on a level surface, N = mg so we have that the applied force = us mg
solving for us: us = applied force/mg = 88N/24kg*9.8m/s/s = 0.37
if it is moving at constant speed, the applied force equals friction, and we have
applied force = uk mg or uk = 51N/24kg * 9.8m/s/s = 0.22
the frictional force = us N where us is the coeff of static friction and N is the normal force
on a level surface, N = mg so we have that the applied force = us mg
solving for us: us = applied force/mg = 88N/24kg*9.8m/s/s = 0.37
if it is moving at constant speed, the applied force equals friction, and we have
applied force = uk mg or uk = 51N/24kg * 9.8m/s/s = 0.22