Question

A man of mass m speeds up while running from rest to a speed v in a straight track along an inclined plane, after rising through a height h.
$W_{gravity}$ = work done by gravity on the man.
$W_{friction}$ = work done by gravity 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

• A. $W_{friction}$ > 0
• B. $W_{friction}=-mgh+\frac{1}{2}m{v}^2$
• C. Work done by the man can be positive, negative or zero
• D. $W_{friction}$ + $W_{man}=-mgh+\frac{1}{2}m{v}^2$

Answer 1

Answer: (C), (D)

Work done by the man can be positive, negative or zero
$W_{friction}$ + $W_{man}=-mgh+\frac{1}{2}m{v}^2$

Work done by the man can be positive, negative or zero because if the total displacement is zero or force is acting perpendicular then work done is zero. If the direction of force is opposite then work done is negative and if in the same direction then the work done is positive.

$W_{friction}+W_{man}=-mgh+\frac{1}{2}m{v}^2.$

Because friction force is always negative and the kinetic motion of man is converted into kinetic energy.

Hence, the correct options are C and D.