Question

No work is done on a suitcase if a man holding it walks on a horizontal paltform but work is done on suitcase when he climbs a staircase why?

Answer 1

because load carries on platform perpendicular to ground .hence work is 0

Answer 2

no work is done on a suitcase if a man holding it walks on a horizontal plane because man is on the same height while he walks on horizontal plane.
But if climbs on a staircase he attends some height due to this work is done