Thread: Physics - Friction

A block weighing 21 N is held at rest against a vertical wall by a
horizontal force of magnitude 59 N. The coefficient of static
friction between the wall and the block is 0.56, and the coefficient of
kinetic friction between them is 0.37. A second
force is applied to the block and directed parallel to
the wall with this magnitude and direction: 62 N, up. What is the
frictional force on the block, including sign? Take the direction up the
wall as positive, and down the wall as negative. Next, calculate the
acceleration, including sign, of the block.


Thanks for any help!

Originally Posted by anywho

A block weighing 21 N is held at rest against a vertical wall by a
horizontal force of magnitude 59 N. The coefficient of static
friction between the wall and the block is 0.56, and the coefficient of
kinetic friction between them is 0.37. A second
force is applied to the block and directed parallel to
the wall with this magnitude and direction: 62 N, up. What is the
frictional force on the block, including sign? Take the direction up the
wall as positive, and down the wall as negative. Next, calculate the
acceleration, including sign, of the block.

Horizontal force is balanced by the normal reaction from the wall. Since the block is at rest, frictional force must be equal to 21 N acting in the upward direction.
when the block is pushed up, Net force acting on it is
P - mg -μ(k)*N = m*a
Now find a. Here m = (21/g) kg