A ball thrown upwards passes a window on the way up and again on the way down. How do its velocities at that window compare?

1. The ball is in free fall, so the same constant acceleration acts on both legs of the trip. 2. That means the speed the ball has at a given height on the way up returns at the same height on the way down. 3. The direction is the one thing that changes, since the ball is rising the first time and falling the second. 4. So the two velocities have equal magnitude and opposite direction. 5. If the speeds differed, energy would have to be lost, and air resistance is being ignored here. _Source: Siyavula Physical Sciences Grade 12 (Everything Science, CC BY 4.0), Chapter 3: Vertical projectile motion in one dimension_