In which of the following cases is the work done positive or zero or negative?a) Work done by the porter on a suitcase in lifting it from the platform on to his head.b) Work done by the force of gr...

Question

In which of the following cases is the work done positive or zero or negative?
a) Work done by the porter on a suitcase in lifting it from the platform on to his head.

b) Work done by the force of gravity on suitcase as the suitcase falls from porter’s head.

c) Work done by the porter standing on platform with suitcase on his head.

d) Work done by force of gravity on a ball thrown up vertically up into the sky.

e) Work done by force applied by hands of a man swimming in a pond.

Philoid · Accepted Answer

a) Positive as the porter apply force on the suitcase in its direction of motion.

b) Positive as the gravity acts downward and suitcase is also falling downward

c) Zero Work is done as force exerted by its head on suitcase cause no motion.

d) Negative as the gravity acts downward and ball is moving upward.

e) Negative as the swimmer propels his hands back so as to get a forward displacement.