A man of mass `m` speeds up while running from rest to a speed v in a straight track along an inclined plane, after raising through a height `h`.
`W_(gravity)="work done by gravity on the man"`
`W_(friction)="work done by friction on the man"`
`W_(man)="work done by man"`
If instead of moving up the plane, the man increases his speed to the value v while moving down the inclined plane through the same vertical distance h, then

Options

A. (a) `W_(f riction)gt0`
B. (b) `W_(f riction)=-mgh+1/2mv^2`
C. (c) Work done by the man can be positive, negative or zero
D. (d) `W_(f riction)+W_(man)=-mgh+1/2mv^2`

Answer

C, D

Explanation

Work done by friction here will also be zero.
Work done by man `=DeltaKE+DeltaPE=1/2mv^2-mgh`
It can be positive, zero, or negative depending upon the value of v and h.