Question

10. Can the direction of the net force acting on an object be opposite to that of its acceleration?

Answer 1

Generally not.

Explanation:

The net force can certainly be in the opposite direction to the velocity (an object decelerating) but as net force is the cause of acceleration, it cannot normally be in the opposite direction.

I did read an article (here: https://phys.org/news/2017-04-physicists-negative-mass.html) describing a Bose-Einstein condensate that seemed to show negative acceleration, implying negative mass, but am not aware that it has been repeated by another team, so remains unconfirmed.