A ball is thrown from ground level vertically upwards with an initial velocity of vi. Draw a velocity-time graph of the ball’s motion. Consider collisions with the ground are absolutely elastic and neglect air resistance.
We assume that the only force acting on an object is the force of gravity which causes it to accelerate towards the center of the Earth at a constant rate of 9.8 m/s^2. We refer the motion to the vertical y axis with +y vertically up. Consequently, the acceleration has to be negative, the velocity is positive when the object is rising and is negative when the object is falling. Also, the acceleration is equal to the slope of the velocity versus time graph.