Work is being done in which of these situations? all motions are at a constant velocity (including velocity = zero).

a.)jessica pushes a 25 kilogram cart a distance of 10 meters.
b.)bane carries a 20 kilogram box a distance of 50 meters.
c.)a weightlifter holds a 100 kilogram barbell over his head.
d.)ali is trying to push a truck away from the parking lot.
e.)yana carries a 5 kilogram bag a distance of 1 kilometer.

None of the above

Explanation:

Work is defined as the force that moves an object through a particular distance:

    Workdone = force x displacement

At constant velocity, the force on a body is zero because such a body is not accelerating.  

    Force is a product of mass and acceleration. Acceleration occurs only when velocity changes with time. If no change in velocity, acceleration does not occur. Therefore, no force is being applied.

 From all the situations given, the condition is set at constant velocity. At constant velocity, there is no acceleration. This implies that no work is done.