In which one of the following situations is zero net work done?
a) a bunch of bananas are placed on a spring scale in the supermarket.
b) a horse pulls a wagon at a constant velocity
c) a sky diver falls from an airplane before opening her parachute
d) a snowball rolls down a hill e a skateboarder steps on a skateboard and begins to roll

b) a horse pulls a wagon at a constant velocity

Explanation:

As we know that ,work done is the dot product of force vector and displacement vector.

W= F.d

W=work

F=Force

d=Displacement

We also know that

F = m a

m= mass ,a = acceleration

When velocity is constant then rate of change in the velocity will be zero,then we can say that acceleration will be zero.

When a= 0  Then F= 0

W= F.d  ( F=0)

W = 0

Therefore option b i correct because horse is going with constant velocity.