Ball Motion from Velocity-Time Graph · CAP 2007 #4
Physics · mechanics
Problem
The graph on the right shows a velocity versus time graph for a ball. [Figure: Velocity-time graph showing initial velocity +v₁, dropping to zero, then to -v₁] Which explanation best fits the motion of the ball as shown by the graph? (a) The ball falls, is caught, and is thrown down with a greater velocity. (b) The ball rises, hits the ceiling, and falls down. (c) The ball falls, hits the floor, and bounces up. (d) The ball rises, is caught, and then is thrown down.Intuitive explanation
The key is reading a velocity-time graph: positive velocity means upward motion, negative means downward, and the direction change tells you when the ball reversed course. Notice the velocity goes from positive to negative with the same magnitude—this symmetry suggests an elastic collision where the ball's speed stays the same but direction flips instantly. That sudden reversal at is the hallmark of a bounce or impact, not a gradual catch-and-throw.
Intuitive explanation
The key is reading a velocity-time graph: positive velocity means upward motion, negative means downward, and the direction change tells you when the ball reversed course. Notice the velocity goes from positive to negative with the same magnitude—this symmetry suggests an elastic collision where the ball's speed stays the same but direction flips instantly. That sudden reversal at is the hallmark of a bounce or impact, not a gradual catch-and-throw.