Conceptual Questions

ssm Solution is in the Student Solutions Manual

| 1 | The speed of light in water is c/n, where n = 1.33 is the index of refraction of water. Thus, the speed of light in water is less than c. Why doesn’t this violate the speed of light postulate?

| 2 | ssm A baseball player at home plate hits a pop fly straight up (the beginning event) that is caught by the catcher at home plate (the ending event). Which of the following observers record(s) the proper time in terval between the two events: (a) a spectator sitting in the stands, (b) a spectator sitting on the couch and watching the game on TV, and (c) the third baseman running in to cover the play? Explain your answers.

| 3 | The earth spins on its axis once each day. To a person viewing the earth from an inertial reference frame in space, which clock runs slower, a clock at the north pole or one at the equator? Why? (Ignore the orbital motion of the earth about the sun.)

| 4 | Suppose you are standing at a railroad crossing, watching a train go by. (a) Both you and a passenger in the train are looking at a clock on the train. Which of you measures the proper time interval? (b) Who measures the proper length of the train car? (c) Who mea sures the proper distance between the railroad ties under the track? Justify your answers.

| 5 | There are tables that list data for the various particles of matter that physicists have discovered. Often, such tables list the masses of the particles in units of energy, such as in MeV (million electron volts), rather than in kilograms. Why is this possible?

| 6 | Why is it easier to accelerate an electron to a speed that is close to the speed of light, compared to accelerating a proton to the same speed?

| 7 | ssm Light travels in water at a speed of . It is possible, in principle, for a particle that has mass to travel through water at a faster speed than this. In what sense, then, does the speed of light represent the ultimate speed attainable by objects that have mass?

| 8 | Review Conceptual Example 9 for background pertinent to this question. Do two positive electric charges separated by a finite distance have more mass than when they are infinitely far apart (assume that the charges remain stationary)? Provide a reason for your answer.

| 9 | Review Conceptual Example 9 for background relevant to this question. One system consists of two stationary electrons, separated by a distance r. Another consists of a positron and an electron, both stationary and separated by the same distance r. A positron has the same mass as an electron, but it has a positive electric charge +e. Which system of charges, if either, has the greater mass? Provide a reason for your answer.

| 10 | Review Conceptual Example 9 for background pertinent to this question. Suppose that a parallel plate capacitor is initially un charged. The capacitor is charged up by removing electrons from one plate and placing them on the other plate. Does the uncharged or the charged capacitor, if either, have the greater mass? Why?

| 11 | The speed limit on many interstate highways is 65 miles per hour. If the speed of light were 65 miles per hour, would you be able to drive at the speed limit? Give your reasoning.

| 12 | Review Conceptual Example 11 as an aid in answering this question. A person is approaching you in a truck that is traveling very close to the speed of light. This person throws a baseball toward you. Relative to the truck, the ball is thrown with a speed nearly equal to the speed of light, so the person on the truck sees the baseball move away from the truck at a very high speed. Yet you see the baseball move away from the truck very slowly. Why? Use the velocity-addition formula to guide your thinking.

| 13 | ssm Which of the following quantities will two observers always measure to be the same, regardless of the relative velocity between the observers: (a) the time interval between two events; (b) the length of an object; (c) the speed of light in a vacuum; (d) the relative speed between the observers? In each case, give a reason for your answer.

| 14 | If the speed of light were infinitely large instead of , would the effects of time dilation and length contraction be observable? Explain, using the equations presented in the text to support your reasoning.

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