A box of books has a mass of 46kg and is being towed by a rope which is oriented at 15 degree to the horizontal at a point where it is tied into a knot. If the pulling force is increased until the box begins to slide, determine the box's initial acceleration if the coefficient of static friction is 0.4 and the coefficient of dynamic friction is 0.25

Answer 1

at the point where it has acceleration = a and velocity = 0, I assume the static friction rules.

normal force = m g - F sin 15

friction force = .4(mg-F sin 15)

pull force horizontal = F cos 15

so
Fcos15 -.4(mg-F sin 15)= m a

Answer 2

-60