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# Physics: Energy conversions, mechanical energy, elastic vs inelastic, initial speed, torques, energy required, angular speed, doppler effect

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A ball dropped to the floor rises to a height less than its original height. Discuss some of the energy conversions that take place in a system like this.

When a mass is placed on top of a vertical spring, the spring compresses and the mass moves downward. Discuss this system in terms of mechanical energy.

Your car rolls slowly in a parking lot and bangs into the metal base of a light pole. In terms of safety, is it better for your collision with the light pole to be elastic or inelastic? Explain

At the grocery store you pick up a can of beef broth and a can of chunky beef stew. The cans are identical in diameter and weight. Rolling both of them down the aisle with the same initial speed, you notice that the can of chunky stew rolls much farther than the can of broth. Why?

When a motorcycle accelerates rapidly from a stop it sometimes "pops a wheelie"; that is, its front wheel may lift off the ground. Explain this behavior in terms of torques

A beetle sits near the rim of a turntable that is at rest, but is free to rotate about a vertical axis. What happens if the beetle begins to walk around the perimeter of the turntable? Does the beetle move relative to the ground? Consider the limits of a very massive turntable and a very light turntable.

Is the amount of energy required to get a spacecraft from the Earth to the Moon greater than, less than, or the same as the energy required to go from the Moon to the Earth? Explain.

A person rides on a Ferris wheel that rotates with constant angular speed. If the Sun is directly overhead, does the person's shadow on the ground undergo periodic motion? Does it undergo simple harmonic motion? Explain.

A "radar gun" is often used to measure the speed of a major league pitch by reflecting a beam of radio waves off a moving ball. Describe how the Doppler Effect can give the speed of the ball from a measurement of the frequency of the reflected beam

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A ball dropped to the floor rises to a height less than its original height. Discuss some of the energy conversions that take place in a system like this.
Sol: When the ball hits the floor each successive time, some of the energy gets transferred to the floor as impact and heat energy. Further, some of the energy is expended in moving against air friction. Therefore, each successive time, the ball rises to a lower height because of energy losses.

When a mass is placed on top of a vertical spring, the spring compresses and the mass moves downward. Discuss this system in terms of mechanical energy.
Sol: Because of its weight, which gives its potential energy, the mass moves down on the spring and the spring is compressed. Now, as the mass goes down, it loses its potential energy (mgh) which gets stored as the spring energy (Â½kx2). When the spring rebounds, the energy stored in it converts back into mass's potential energy and the mass rises again.

Your car rolls slowly in a parking lot and bangs into the metal base of a ...

#### Solution Summary

In a 782 word solution, the concepts and explanations carefully answer all the questions.

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