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Question

A man pushes a 15 kg box of books 2.0 m up a 37 incline into the back of a moving van. The box moves at a constant velocity if you push it with a force of 95 N. Find the work done by gravity on the box. Take (g=10 m/s2)
  1. 180 J
  2. 180 J
  3. 120 J
  4. Zero


Solution

The correct option is A 180 J
FBD  of system is

From FBD of the block, we have the component of weight down the incline plane as mgsinθ and the displacment is up the incline plane d=2.0 m, the other component of weight will be perpendicular to plane mgcosθ.

Now here the work done will be due to the force component along the plane only which is, F=mgsinθ.
The angle between F and d  is  180o

Hence  work done by gravity will be only due to the force along the incline plane Wg=F.s=(mgsin37o)×2×cos180o

Wg=180 J

Hence option A is the correct answer

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