Question

Right at the midpoint of its motion, the cart has zero acceleration, because the net force on it is zero. So, why doesn’t the cart stay at constant velocity after reaching that point?

Answer 1

The acceleration could change after it reaches the midpoint of its motion. so the velocity would be constant only for an instant of time

Answer 2

so i would say, because the acceleration does not have to stay at zero, after reaching the midpoint