5.11. a)
The rope makes an angle of 
with the x axis. Summing the forces in the y
direction yields
From which we find that the magnitude of the normal force, n, is 19.1 N. That leads us to the force of kinetic friction, which we find is
From the x components, we find that
or, 
b)
Now, we want to find the angle at which the acceleration is zero. In the x direction,
and the force of friction is given by
So, applying the quadratic formula, we find that
or, 
The negative root to this would imply that the pulley was below the
block, but we know that it is above it, so only consider the positive
value. Then, to find the x distance, we take the tangent of our
angle 
.
or, x = 6.10 cm