A ball is dropped from a height h. Just before it hits the ground, its speed is
Correct answer: A. the square root of 2gh
- A. the square root of 2gh
- B. 2gh
- C. gh
- D. the square root of gh
Explanation
Equating the potential energy mgh to the kinetic energy half mv squared cancels the mass and gives v as the square root of 2gh, which is why all bodies fall at the same rate in the absence of air resistance. The same result follows from the equations of motion. Doubling the height increases the landing speed only by a factor of the square root of two.
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About Potential Energy
Potential energy is energy stored because of position or configuration, including gravitational potential energy near Earth's surface and elastic energy in a stretched or compressed spring. Questions use changes in potential energy and conservation of mechanical energy, while distinguishing a chosen reference level from an absolute zero of energy.
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