help ...please...thanks ...A 12 N horizontal force F pushes a block weighing 5.0 N against a vertical wall. The coefficient of static friction between the wall and the block is 0.60, and the coefficient of kinetic friction is 0.40. Assume that the block is not moving initially. (a) will the block move? (b) in unit-vector notation, what is the force on the block from the wall?

Question

help ...please...thanks ...>>>>>>A 12 N horizontal force F pushes a block weighing 5.0 N against a vertical wall. The coefficient of static friction between the wall and the block is 0.60, and the coefficient of kinetic friction is 0.40. Assume that the block is not moving initially. (a) will the block move? (b) in unit-vector notation, what is the force on the block from the wall?

anonymous · Answer

You need to counter the weight 5N by friction which is given by 0.6* Pushing-Force

anonymous · Answer

friction = 0.6*NormalForce

anonymous · Answer

NormalForce = Pushing Force = 12 N

anonymous · Answer

Soooo friction = ?....

anonymous · Answer

|dw:1346220868332:dw|f is friction, $$f= \mu R$$and since the block is pushed into the wall by a force of 12N, $$R=12N$$$$\mu = 0.6$$which gives us$$f=0.6\times12$$for the block to not move this friction has to be equal to the weight. Check if $$ f=mg$$if yes, then the block does not move. 
Part (b) the force on the block by the wall = - force on the wall due to the block( according to Newton's third law), assume that the direction of the applied force of 12N is positive x, so $$F = 12 \hat i$$, use this to get the answer.