Which movement has the greatest net work done?

[songoku]

Homework Statement

Please see below

Relevant Equations

W = F.d

My answer is (D) but the answer key is (C).

My reasoning is that the net work for (A), (B) and (C) are all zero since the object moves with constant speed so the resultant force is also zero. What is the mistake in my reasoning?

Thanks

 

[kuruman]

Have you considered the possibility that the answer key might be in error?

 

[songoku]

Have you considered the possibility that the answer key might be in error?

Yes, but knowing me, it is better to ask for confirmation here.

Thank you very much kuruman

 

[haruspex]

I thought this question was familiar, even in that the official answer is wrong. https://www.physicsforums.com/threa...ted-on-a-conveyor-belt-with-friction.1061325/