A block of mass `10kg` is released on a fixed wedge inside a cart which is moved with constant velocity `10m//s` towards right. Take initial velocity of block with respect to cart zero. Then work done by normal reaction (with respect to ground) on block in two second will be `:(g=10 m//s^(2))`.

Options

A. zero
B. 960 J
C. 1200 J
D. none of these

Answer

B

Explanation

Because the acceleration of wedge is zero. The normal reaction exerted by wedge on block is
`N = mg cos 37^(@)`
The acceleration of the block is `g sin 37^(@)` along the incline and initial velocity of the block is `v = 10 m//s` horizontally towards right as shown in figure.

The component of velocity of the block normal to the incline is `v sin 37^(@)`. Hence the displacement of the block normal to the incline in t = 2 second is
`S=v sin 37^(@) xx 2 = 10 xx (3)/(5) xx 2 =12 m`
`:.` The work done by normal reaction
`W = mg cos 37^(@) S = 100 xx (4)/(5) xx 12 = 960 J`