# Re: Physics/Math

posted by
**COFFEE** on
.

A 17 N horizontal force F pushes a block weighing 6.0 N against a vertical wall. The coefficient of static friction between the wall and the block is 0.68, and the coefficient of kinetic friction is 0.48. Assume that the block is not moving initially. Will the block move? In unit-vector notation, what is the force exerted on the block by the wall?

* Physics/Math - bobpursley, Saturday, February 10, 2007 at 7:10pm

Force friction= mu*17= 11.6N

weight= 6N. Force of friction prevents it from moving.

Ok, so in unit-vector notation the force would be (11.56 N)i + (0 N)j???

No. The wall exerts friction upward, and exerts a counter force of 17 N horizontally.

As a matter of clarification, the force of friction is not 11.6 N, it is 6 N exactly equaling the block weight. The formula mu*force normal is the maximum friction. (f it were greater then 6N the block would move upward, which is not going to happen.

Well if it will not move upward then wouldn't the i component for the final answer be 0 N? That's what I thought it would be but it is incorrect so I am stuck.

the force exerted by the wall, according to newton, would be an equal and opposite reaction, so for the i direction it would be the negative of the force the block places on the wall. the j direction would be the weight of the block