Question

A man holds and displaces a 20kg mass horizontally in his stretched hand . (a) he does zero work against force of gravity (b) he does 200 joules of work per metre (c) the work done against gravity is equal to the muscular energy (d) the work done against gravity cannot to estimated but non-zero

Answer 1

answer : option (a) he does zero work against force of gravity.

explanation : we know, work done is the dot product of force and displacement.

so, W = F.scosθ

according to question, A man holds and displaces a 20kg mass horizontally in his hand.

so, gravitational force acting on body, F = mg = 20kg × 9.8 m/s² = 196N (downward direction)

and displacement, s along horizontal direction.

then, angle between displacement and force , θ = 90°

so, workdone , W = 196 × s cos90° = 0

hence, work done against force of gravity is zero.

Answer 2

Explanation:

hope this answer is right and helps you