Question

which action is not an example of work? pushing a box across the floor raising a barbell over your head picking up a box off the floor holding a tray in the cafeteria line

Explanation:

Work is defined as the product of force and displacement in the direction of the force ($W = F\times d$). When pushing a box across the floor, raising a barbell, or picking up a box, there is a force applied and a displacement in the direction of the force. However, when holding a tray in the cafeteria line, there is a force (the force to hold up the tray) but no displacement in the direction of the force.

Answer:

holding a tray in the cafeteria line