A box with mass 5.0 kg is initially at rest at point A at the bottom of a 8.0 m

Question

A box with mass 5.0 kg is initially at rest at point A at the bottom of a 8.0 m long ramp that isinclined at an angle of 53.00 above the horizontal. A worker applies a constant force F=90 N thatis parallel to the ramp and directed up the ramp in order to pull the box to the top of the ramp (point B). While the box ismoving, the ramp exerts a constant friction force of 18.0 N on the box, directed down the ramp.

a) For the motion of the box from point A to point B, what the work done on the box by gravity?

b) For the motion of the box from point A to point B, what is the work done on the box by the normal force thatis exerted on the box by the ramp?

c). For the motion of the box from point Ato point B, what isthe work done on the box by the friction force thatthe ramp exerts on the box?

Explanation / Answer

a) Work by gravity = mglsin53 = 5 x 9.81 x 8 x sin53 =313.38 J

b) normal force is perpendicular to displacement so N.d = Ndcos90 = 0 .

c) w = F.d = 18 x 8 =144N

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