A force of 15 N is required to pull up a body of mass 2 kg through a distance of 5m along an inclined plane making an angle of 30 degree with the horizontal. (If you need, I can give the figure with the question.) Calculate:
1)the work done by the force in pulling the body
2)the work done against the force due to gravity (g=9.8 N/kg)
3)account for the difference in the magnitude of the above two readings.
Work=Force*Displacement*cosine of the angle
The Attempt at a Solution
Part 1) Work done =15*5=75 J as the force and displacement are in the same direction, i.e., 30 degree with the horizontal)
Part 2)Work done against gravity=mgh=2*9.8*(5*cos30)=49 J
5*cos 30, give the vertical displacement.
Part 3) Here lies the problem, I think that the difference is because, in first case we consider vertical displacement and the horizontal one, I mean both the components, so the work done is more. In the second case, only the vertical component counts, both for the force and the displacement.
My book gives a vague answer to this,
Please help me with part 3. I will provide the figure given with this question if it is needed but you. But please do try to help.The difference in work=(75-49)=16 J is utilised in doing work against friction between the body and the inclined plane.