Crate pulled horizontally

Good evening.

I would appreciate if someone could verify the following please.

The question:

A 100kg crate is pulled across a horizontal floor by a force P that makes an
angle of 30 degrees above the horizontal. The coefficient of kinetic
friction between the crate and floor is 0.200. What is P if the net work
done is zero.

My solution:

First determine Ff = umg. This would give me 196N. My next step is to
determine P. I use 196N and put that over cos30. My answer is 226.3N. Does
this seem reasonable.

thanks for your time

TGen wrote:

snip

A 100kg crate is pulled across a horizontal floor by a force P that
makes an
angle of 30 degrees above the horizontal. The coefficient of kinetic
friction between the crate and floor is 0.200. What is P if the net
work
done is zero.

Trick questions?

If the net work [W = force * distance] = 0, then either the force is
zero or the distance is zero.

Since the crate is "pulled" the force is obviously NOT zero, so the
distance must be zero. This means that the "pull" is insufficient to
budge the crate.

You are given the coefficient of *kinetic* friction, but if the crate
doesn't move, there is nothing "kinetic" about this problem. What you
need is the coefficient of *static* friction. Then you can determine
an _upper limit_ to the applied force, so that if any more force is
applied than determined by the limit the crate *will* move.

Either that, or you have incorrectly restated the problem...
..
..
Tom Davidson
Richmond, VA