Work requires net force parallel to displacement

Steps:

• Define work as $W = \vec{F} \cdot \vec{d} = F d \cos\theta$, where positive work occurs if force and displacement align.
• Evaluate each option for applied force and object motion.
• Identify scenarios with zero displacement or zero net force component along motion.
• Select the case with clear force and parallel displacement.

Why C is correct:

• Pushing applies force with a component parallel to the ramp's displacement, so $W = F_\parallel d > 0$ by work-energy theorem.

Why the others are wrong:

• A: Constant velocity on frictionless surface means net force is zero, so no work done.
• B: Object is held stationary, so displacement $d = 0$, work is zero.
• D: Object is stationary while floating, so displacement $d = 0$, work is zero.

Final answer: C