# Unit 10 Extra Credit

Either print this page and complete or (better yet) neatly show your answers on a separate page of paper. All answers must be expressed as complete sentences and/or all work shown to receive credit

1. When a wave reaches the boundary of a new medium, part of the wave is reflected and part is transmitted. What determines the amount of reflection?

2. When a wave crosses a boundary between thin and thick rope, its wavelength and velocity change, but its frequency does not. Explain why the frequency is constant.

3. Joe makes a single pulse on a stretched spring. How much energy is required to make a pulse with twice the amplitude?

4. The Sears Building in Chicago sways back and forth with a frequency of about 0.10 Hz. What is its period of vibration?

5. An ocean wave has length of 10.0 m. A wave passes a fixed location every 2.0 s. What is the speed of the wave?

6. A group of swimmers is resting in the sun on an off-shore raft. They estimate that 3.0 m separates a trough and an adjacent crest of surface waves on the lake. They count 14 crests that pass by the raft in 20 s. How fast are the waves moving?

7. AM radio signals are broadcast at frequencies between 550 kHz and 1600 kHz (kilohertz) and travel 3.0 X 10^8 m/s.

a. What is the range of wavelengths for these signals?

b. FM frequencies range between 88 MHz and 108 Mhz (megahertz) and travel the same speed. What is the range of FM wavelengths?

8. The speed of sound in water in 1498 m/s. A sonar signal is sent from a ship at a point just below the water surface and 1.80 s later the reflected signal is detected. How deep is the ocean beneath the ship?

9. The velocity of the transverse waves produced by an earthquake is 8.9 km/s, while that of the longitudinal waves is 5.1 km/s. A seismograph records the arrival of the transverse waves 73 s before that of the longitudinal waves. How far away was the earthquake?

10. The time needed for a water wave to change from the equilibrium level to the crest is 0.18 s.

a. What fraction of a wavelength is this?

b. What is the period of the wave?

c. What is the frequency of the wave?

11. If you slosh the water back and forth in a bathtub at the correct frequency, the water rises first at one end and then at the other. Suppose you can make a standing wave in a 150-cm long tub with a frequency of 0.3 Hz. What is the velocity of the water wave?

Resources for physics students are available through links on the GBS Physics Home Page. Such resources include the Multimedia Physics Studios (a collection of animations and movies which illustrate key physics concepts) and The Physics Classroom (an online tutorial written in an easy-to-understand language).