A block has an initial kinetic energy of 128 J. It slides up from point A at the bottom of the inclined plane with uniform deceleration. When it passes point B , its kinetic energy is reduced by 80 J

Question

A block has an initial kinetic energy of 128 J. It slides up from point A at the bottom of the inclined plane with uniform deceleration. When it passes point B , its kinetic energy is reduced by 80 J , and its mechanical energy is reduced by 35 J . Calculate the work done against friction when the block moves from A to the highest point C on the inclined plane.

TestHub · Accepted Answer

A to B: KE drops 80 J; friction takes 35 J of it, so the PE gain is 45 J. Deceleration is uniform, hence friction and the gravity component are constant along the plane: their works split any further travel in the same 45 : 35 ratio.

B to C consumes the remaining 48 J of KE, of which friction takes $48 \times \frac{35}{80} = 21 J$ .

$W_{friction} = 35 + 21 = 56 J$

Ans. (C)

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