Conceptual Physics (12th Edition)

Published by Addison-Wesley
ISBN 10: 0321909100
ISBN 13: 978-0-32190-910-7

Chapter 10 - Think and Explain: 61

Answer

When the cannonball is fired at low speed, it moves forward and down. Earth gravity has a component in the direction of the ball's motion, does positive work, and speeds the ball up. At a high enough speed, the cannonball's falling distance matches Earth's curvature so that the cannonball always moves parallel to the surface, at right angles to gravity. When a force acts perpendicular to an object's direction of motion, it does no work and does not change its KE.

Work Step by Step

This is discussed on pages 190-191.
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