What minimum force would you need to apply to do work against gravity without accelerating an object?

Question

The way this question was worded is strange. The object is placed at a height of 5m on a frictionless surface and it is let go. It travels the U-shaped track back and forth. How can there be no acceleration if the velocity is changing as the object moves up and down/back and forth? Also there is no mass and no angle to the incline so I'm assuming there is no way to come up with a numerical answer. I cant understand though the force needed to do work against gravity without accelerating the object. Also I know that there is no work done against gravity when moving horizontally however there is a vertical component to this since it travels up and down the track as well.

Answer 1

The answer to the question is the weight.

If there is a change in velocity (either change in magnitude or direction or both) there is acceleration.