Exploration 7.2: Choice of Zero for Potential Energy
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The animation depicts a ball being dropped from y = 15 m onto the ground 15 meters below at y = 0 m (position is given in meters and time is given in seconds). For this animation we will assume that the ball undergoes a very hard collision with the ground, which also conserves energy. Also shown are two pairs of bar graphs representing the different types of energy associated with the ball: the kinetic energy (orange) and the gravitational potential energy (blue). The bar graphs on the left show the kinetic energy and the potential energy as measured from yref = 0 m. The bar graphs on the right show the kinetic energy and the potential energy with a varying zero potential energy point. You can vary the zero point from -15 m < yref < 15 m by changing the value in the text box and clicking the "set value and play" button. Restart.
Change the zero point for the potential energy from zero to a variety of positive values and a variety of negative values. Answer the following questions about the animation.
- For zero points that are less than zero, does the gravitational potential energy shift up or down?
- Is all of this energy accessible to the ball? In other words, can it all be converted to kinetic energy?
- For zero points that are greater than zero, does the gravitational potential energy shift up or down?
- For yref = -15 m, how much potential energy does the ball start out with? How much does it have when it hits the ground? What is the change in potential energy?
- For yref = 15 m, how much potential energy does the ball start out with? How much does it have when it hits the ground? What is the change in potential energy?
- How do your answers for (d) and (e) compare? Why?