What is the Optimal Angle for Pulling a Crate Across a Rough Floor?

[eriadoc]

Homework Statement

A man wishes to pull a crate 15m across a rough floor by exerting a force of 100N. The coefficient of kinetic friction is 0.25. For the man to do the least amount of work, the angle between the force and the horizontal should be:

Homework Equations

W=Fd; frictional force=coefficient of friction * Normal force;

The Attempt at a Solution

The answer is 66 degrees, which doesn't seem like an answer that would come up on a conceptual problem. Without the mass of the crate, I don't know how to do this problem at all. Even with the mass, I'm not all that sure, to be honest. W=1500 N/m, but that doesn't really do anything for me. The coefficient of friction is sort of useless without being able to calculate the normal force. I'm really just hopelessly lost on this one. Any hints to get me thinking in the right direction would be greatly appreciated. Thanks.

 

[eriadoc]

OK, turns out my instructor screwed up on the answer key and put 66 degrees as the answer, thus confusing everyone in his class. It's zero, as we all thought.

Disregard this post.