Force on a box?

Question

You push with a horizontal force of 38.7 N against a 19.0 N box, pressing it against a rough wall to hold it in place. The coefficients of kinetic and static friction between this box and the wall are 0.300 and 0.600, respectively.

A) What is the friction force on the box?

B) How hard would you have to press for the box to slide downward with a uniform speed of 8.50 cm/s?

Anonymous · Accepted Answer

a)  Force of friction = mu force normal

= (mu) * (your horizontal push force)

b)  To travel at a constant velocity, the net force must be zero, so friction and the weight must be equal and opposite.

Friction force = mu (push force) = weight

So push = weight / mu

For part (a), since the block is still, use the static mu.  For part (b), the block is moving, so use the kinetic mu.

Force on a box?

1 Answer