# static friction problem

• Oct 15th 2007, 01:21 PM
rcmango
static friction problem
heres the question:

A bedroom bureau with a mass of 47 kg, including drawers and clothing, rests on the horizontal floor. The coefficient of static friction between the bureau and the floor is 0.45 and nothing except the floor is touching the bureau initially.

need to know

the static friction force on the bureau initially?
in Newtons

Now you pull horizontally with a force of 83 N. What is the magnitude of the static frictional force?
in Newtons

and then What minimum horizontal force must you apply to start the bureau moving?
in Newtons

• Oct 15th 2007, 01:31 PM
topsquark
Quote:

Originally Posted by rcmango
heres the question:

A bedroom bureau with a mass of 47 kg, including drawers and clothing, rests on the horizontal floor. The coefficient of static friction between the bureau and the floor is 0.45 and nothing except the floor is touching the bureau initially.

need to know

the static friction force on the bureau initially?
in Newtons

The static friction force is no larger than it needs to be, up to the maximum value.

So draw a Free-Body Diagram. What forces are on the bureau? (Hint: if there are no applied horizontal forces on the bureau, what does the static friction force have to be in order for it not to move sideways?)

Quote:

Originally Posted by rcmango
Now you pull horizontally with a force of 83 N. What is the magnitude of the static frictional force?
in Newtons

Now you have an applied horizontal force. Is this force greater than the maximum for the static friction? Again, refer to the FBD and recall that $f_{s,max} = \mu _s N$. If the applied force is not greater than the maximum static friction force, how large does the friction force have to be to keep the bureau in place?

Quote:

Originally Posted by rcmango
and then What minimum horizontal force must you apply to start the bureau moving?
in Newtons

For this one you have to apply a force that exceeds the maximum for static friction. What force would this be?

-Dan