A block of mass m is directly pulled up slowly on a smooth inclined plane of height h and inclination `theta` with the help of a string parallel to the incline. Which of the following statement is incorrect for the block when it moves up from the bottom to the top the incline? . .

Options

A. Work done by the normal reaction force is zero .
B. Work done by the string is `mgh`
C. Work done by gravity is `mgh`
D. Net work done on the block is zero

Answer

C

Explanation

(a) `W_(N) =NS cos 90^(@) -0`
(b) `W_(T) =TS cos 0^(@) =(mg sin theta) ((h)/(sintheta))`
`=mgh`
(c ) `W_(mg) =(mg) (h) cos180^(@) =-mgh`
(d) `W_("Total") =DeltaK =K_(f)-K_(i) =0`.
As block is moved slowly or `K_(f) =K_(i)`.