under which condition is no work done?\na force pushes an object and slows it down.\na force pulls an object…

Brief Explanations:

Work is calculated as (W = F\times d\times\cos\theta), where (F) is the force, (d) is the displacement, and (\theta) is the angle between the force and displacement vectors. If there is no displacement ((d = 0)), then (W=0). In the case of "A force pushes up on an object that stays in place", the displacement (d = 0). For the other options:

• In "A force pushes an object and slows it down" and "A force pulls an object and speeds it up", there is a non - zero displacement and the force has a component along (or opposite to) the direction of motion.
• In "A force pulls down on an object that moves downward", the force and displacement are in the same direction ((\theta = 0^{\circ}), (\cos\theta=1)), so work is done.

Answer:

A force pushes up on an object that stays in place.