PHYSICS HELP ! a person pushes on a stationary.......?

Question

a person pushes on a stationary 125N box with 75N at 30 degrees below the horizontal. the coefficient of static friction between the box and the horizontal floor is 0.80. What is the normal force on the box? What is the friction force on the box? what is the largest the friction force could be? the person now replaces his push with a 75N pull at 30 degrees above the horizontal.Find the normal force on the box in this case.

Answer 1

The normal force will be the weight minus the upward vertical component of the applied force.

N*u is the maximum force that can be applied in the horizontal before the box will move (u is static friction coefficient)

Since the force is applied at an angle it influences the normal force as:

N=125 - sin(30)*75

N=87.5

So the maximum friction would be

87.5*.8

=70

Since the applied force horizontal component is
cos(30)*75

=65 N

which is less than the maximum, then the frictional force that develops is 65N since the forces must balance.

When the pull is at 30 degrees above, all the force magnitudes are the same. The difference would be in direction only, so if there is a sign convention, set the appropriate sign with respect to the direction.

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