A) An object held 1.5m above the ground.
- Well, it's staying stationary so technically there's no real distance. Distance in terms of Work would be the distance the object moved. This question is only defining distance from the ground. Not really applicable. Also, there doesn't seem to be a force component.
B) Object moves at a constnat velocity (0.5/s horizontally on frictionless surface)
- I'm not too sure about this. Friction was never my favorite part of physics. In order for it to be a work problem you'd have to know at what point it stops (and if it were truly frictionless, wouldn't it not stop?) to find out the distance travelled and it's a constant velocity, not sure if there's any force in that. Also cause force = mass * acceleration. No acceleration, no force, no work.
C) Object falls freely from 1.5m above to the floor.
- I think yes, because the force of gravity is acting on it, which is 9.8 m/s^2. and you have the distnace of 1.5m cuz its actually falling.
So there you go. sorry for the long answer just wanted to make sure you understood everything i was saying and the reasoning. I think your intuition about no acceleration might be correct, since again:
W = Fd
F = ma
and if there's no "a" there's no "f" and no "f' means no "w" as the calculations would keep multiplying to 0.
Like if F = ma, and a = 0, 0 x anything = 0 so f will be zero, and since f is zero w is zero.