Homework

1. Homework • A piano string sounds a middle A by vibrating primarily at 220 Hz. • (a) Calculate the string's period and angular frequency. • (h) Calculate the period and angular frequency for a soprano singing an A one octave higher, which is twice the frequency of the piano string.

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3. Homework • A harmonic oscillator consists of a 0.500-kg mass attached to an ideal spring with force constant 140 N/m. Find (a) the period; (h) the frequency; (c) the angular frequency of the oscillations.

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5. Homework • An object is undergoing SHM with period 1.200 s and amplitude 0.600 m. At t = 0 the object is at x = O. How far is the object from the equilibrium position when t = 0.480 s

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7. Homework • Weighing Astronauts. This procedure has actually been used to "weigh" astronauts in space. A 42.5-kg chair is attached to a spring and allowed to oscillate. When it is empty, the chair takes 1.30 s to make one complete vibration. But with an astronaut sitting in it, with her feet off the floor, the chair takes 2.54 s for one cycle. What is the mass of the astronaut .

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9. Homework • A 1.50-kg mass on a spring has displacement as a function of time given by the equation • x(t) = (7.40 cm)cos[(4.16 S-l)t - 2.42]. • Find (a) the time for one complete vibration; • (b) the force constant of the spring; • (c) the maximum speed of the mass; (d) the maxi- mum force on the mass; (e) the position, speed, and acceleration of the mass at t = 1.00 s; (f) the force on the mass at that time.

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11. Homework • 13.23. A 0.500-kg glider, attached to the end of an ideal spring with force constant k = 450 N/m, undergoes SHM with an amplitude of 0.040 m. Compute (a) the maximum speed of the glider; (b) the speed of the glider when it is at x = -0.015 m; (c) the magnitude of the maximum acceleration of the glider; (d) the acceleration of the glider at x = -0.015 m; (e) the total mechanical energy of the glider at any point in its motion.

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13. Homework • 13.26. A 0.150-kg toy is undergoing SHM on the end of a horizontal spring with force constant k = 300 N/m. When the object is 0.0120 m from its equilibrium position, it is observed to have a speed of 0.300 m/s. What are (a) the total energy of the object at any point of its motion; (b) the amplitude of the motion; (c) the maximum speed attained by the object during its motion?

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15. Homework • 13.31. A l75-g glider on a horizontal, frictionless air track is attached to a fixed ideal spring with force constant 155 N/m. At the instant you make measurements on the glider, it is moving atO.815 m/s and is 3.00 cm from its equilibrium point. Use energy conservation to find (a) the amplitude of the motion and (b) the maximum speed of the glider. (c) What is the angular frequency of the oscillations.

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18. Homework • 13.41- You pull a simple pendulum 0.240 m long to the side through an angle of 3.50 and release it. (a) How much time does it take the pendulum bob to reach its highest speed. (b) How much time does it take if the pendulum is released at an angle of 1.750 instead of 3.50 .

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20. Homework • 13.47- After landing on an unfamiliar planet, a space explorer constructs a simple pendulum of length 50.0 cm. She finds that the pendulum makes 100 complete swings in 136s. What is the value of g on this planet .

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22. Homework • 43.22- Radioactive isotopes used in cancer therapy have a "shelf- life," like pharmaceuticals used in chemotherapy. Just after it has been manufactured in a nuclear reactor, the activity of a sample of 60co is 5000 Ci. When its activity falls below 3500 Ci, it is considered too weak a source to use in treatment. You work in the radiology department of a large hospital. One of these 60co sources in your inventory was manufactured on October 6, 2004. It is now April 6, 2007. Is the source still usable? The half-life of 60co is 5.271 years.

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24. Homework • 43.23, A 12.0-g sample of carbon from living matter decays at the rate of 180.0 decays/min due to the radioactive 14c in it. What will be the decay rate of this sample in (a) 1000 years and (b) 50,000 years?

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26. Homework • 43.24, Radioactive Tracers. Radioactive isotopes are often introduced into the body through the bloodstream. Their spread through the body can then be monitored by detecting the appearance of radiation in different organs. 131I, β- emitter with a half- life of 8.0 d is one such tracer. Suppose a scientist introduces a sample with an activity of 375 Bq and watches it spread to the organs. (a) Assuming that the sample all went to the thyroid gland, what will be the decay rate in that gland 24 d (about 21/2weeks) later? (b) If the decay rate in the thyroid 24 d later is actually measured to be 17.0 Bq, what percentage of the tracer went to that gland? (c) What isotope remains after the 1-131 decays?

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28. Homework • 4325. Tritium (3H) undergoes β- decay with a half-life of 12.3 years. It is also highly toxic to living things. (a) What nucleus is produced in the β- decay of tritium? (b) Suppose some tritium gas is released into the atmosphere in a nuclear power plant • accident. How long will it take for 90.0% of the tritium to become nonradioactive?

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30. Homework • 43.26. As a health physicist, you are being consulted about a spill in a radiochemistry lab. The isotope spilled was 500µCi of 13IBa, which has a half-life of 12 days. (a) What mass of I31Ba was spilled? (b) Your recommendation is to clear the lab until the radiation level has fallen 1.00µCi. How long will the lab have to be closed?

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