What is the work Ww done on the box by the weight of the box?

A box of weight w=2.0N accelerates down a rough plane that is inclined at an angle ϕ=30∘ above the horizontal, as shown (Figure 6) . The normal force acting on the box has a magnitude n=1.7N, the coefficient of kinetic friction between the box and the plane is μk=0.30, and the displacement d⃗ of the box is 1.8 m down the inclined plane.

1 Answer
Nov 13, 2017

OK, first we need to find the force pulling the box down the plane, then figure out the work done.


The friction is given by #F_r = mu.N# where N is the normal reaction, 1.7N

So #F_r = 0.3 xx 1.7 = 0.51# N this points against the motion, so acts up the plane.

The force acting down the plane is given by the component of gravity acting parallel to the plane, #F_a = m.g. sin theta#

#F_a = 2 xx sin 30^@# = 1 N

So the net force, #F = F_a - F_r#

#F = 0.49# N

Work done, W = F.s

So #W = 0.49 xx 1.8#

Thus W = 0.882 or 0.88 Nm to 2 s.f.