Pearson Physics Level 20 Unit IV Oscillatory Motion and Mechanical Waves: Chapter 7 Solutions
Student Book page 345
Example 7.1 Practice Problems 1. Analysis and Solution 60 s T =×5.00 min 1 min = 300 s 1 f = T 1 = 300 s =×3.33 10−3 Hz The frequency of the earthquake waves is 3.33 × 10−3 Hz. 2. Analysis and Solution 1 T = f 1 = 78Hz = 0.013s The period of the hummingbird’s wing is 0.013 s.
Student Book page 347
7.1 Check and Reflect Knowledge 1. For motion to be oscillatory, it must repeat at regular intervals. 2. Equivalent units are revolutions/s and Hz. 3. Period: The time required for one complete oscillation (cycle) Frequency: The number of oscillations (cycles) per second 1 4. T = . They are the inverse of one another. f 5. No, it is not possible. Frequency and period are inversely related to one another, so if the period increases, the frequency must decrease. 6. Students’ answers will vary. Some possible answers could include: clock, wheel, bird/insect wings, planets, toys.
Pearson Physics Solutions Unit IV Chapter 7 1 Copyright © 2007 Pearson Education Canada Applications 7. Analysis and Solution 1rev 1cycle = ss 20.0rev 20.0cycles = ss = 20.0Hz The frequency of the toy is 20.0 Hz. 8. The oars on a rowboat move with oscillatory motion if the rowing motion is at a constant rate. 9. Analysis and Solution 1 f = T 1 = 0.004 00 s =×2.50 102 Hz The guitar string has a frequency of 2.50 × 102 Hz. 10. Analysis and Solution 1 T = f 1 = 38Hz = 0.026s The period of the dragonfly’s wings is 0.026 s. 11. Analysis and Solution 4800 beats 1 min f = × min 60 s = 80.00 Hz 1 T = f 1 = 80.00 Hz = 0.01250 s The period of the bird’s wings is 0.01250 s. 12. (a) Analysis and Solution 1 T = f 1 = 2.50 Hz = 0.400 s The period of the dog’s tail is 0.400 s.
Pearson Physics Solutions Unit IV Chapter 7 2 Copyright © 2007 Pearson Education Canada (b) Analysis and Solution 60 s # wags = 2.50 Hz × 1 min =×1.50 102 wags The dog will wag its tail 1.50 × 102 times in 1 min. Extensions 13. Students’ answers will vary. Possible insects researched could include: Insect Frequency (Hz) Mosquito 550 Housefly 330 Wasp 110 Ladybug (beetle) 46–90 Dragonfly 38 Butterfly 9–12 14. (a) This motion is periodic because the skater performs the same motion at the same speed. (b) This motion can be considered periodic if the car’s speed doesn’t change. In practice, the motion is not periodic because the car’s speed varies. (c) This motion can be considered periodic when a person is at rest, but not when he or she changes the level of physical exertion. 15. Frequency (Hz) (a) fluorescent light 120 Hz bulbs (b) overhead power lines 60 Hz (c) human voice range Approx. 250 Hz– 3000 Hz (d) FM radio range 88 MHz–108 MHz (e) lowest note on a bass 41.2 Hz guitar
Pearson Physics Solutions Unit IV Chapter 7 3 Copyright © 2007 Pearson Education Canada Student Book page 352
Example 7.2 Practice Problems 1. Analysis and Solution Plotting the values gives the following graph:
Force vs. Displacement
The slope is: k = slope (150− 0.0) N = (0.60− 0.0)m =×2.5 102 N/m The spring constant of this spring is 2.5 × 102 N/m. 2. Analysis and Solution Determine the slope (spring constant) by taking two values from the line on the graph. Below is an example of a calculation. Actual values chosen may vary. (30.0− 0.0)N k = (2.0− 0.0)m = 15N/m The spring constant of this spring is 15 N/m.
Pearson Physics Solutions Unit IV Chapter 7 4 Copyright © 2007 Pearson Education Canada Student Book page 354
Example 7.3 Practice Problems 1. Analysis and Solution