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Homework 12

# Homework 12 - Bautista Aldo Homework 12 Due 4:00 am Inst...

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Bautista, Aldo – Homework 12 – Due: Nov 22 2005, 4:00 am – Inst: Maxim Tsoi 1 This print-out should have 26 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. The due time is Central time. 001 (part 1 of 1) 10 points Radio waves travel at the speed of light: 300000 km / s. What is the wavelength of radio waves re- ceived at 106 . 1 MHz on your FM radio dial? Correct answer: 2 . 82752 m. Explanation: Let : v = 300000 km / s = 300 million m / s and f = 106 . 1 MHz = 106 . 1 million Hz . λ = v f = 300 million m / s 106 . 1 million Hz = 2 . 82752 m . 002 (part 1 of 1) 10 points A mass is placed on a spring and oscillates with a period of 1 second. Now a heavier mass is placed on the same spring. Which statements are true? I. The heavier mass oscillates with a shorter period because the gravitational force on it is greater. II. The heavier mass oscillates with the same period because gravitational accel- eration is constant. III. The heavier mass oscillates with a longer period because of its greater iner- tia. IV. The heavier mass must have greater mechanical energy than the first because it is heavier. V. The heavier mass must have less me- chanical energy than the first because it moves more slowly. VI. One cannot reach any conclusion about mechanical energy without know- ing the amplitude of motion in each case. 1. II and V only 2. I and IV only 3. I and V only 4. II and IV only 5. II and VI only 6. I and VI only 7. III and IV only 8. III and V only 9. III and VI only correct Explanation: The mechanical energy of a system is a function of the amplitude of oscillation. Since the amplitude is not given, the mechanical energy is unknown. The heavier mass will alter the angular frequency of the oscillation and the period. T = 2 π r m k So if the mass increases, the period must also increase. 003 (part 1 of 1) 10 points Earthquakes produce two kinds of seismic waves: The longitudinal primary waves (called P waves) and the transverse secondary waves (called S waves). Both S waves and P waves travel through Earth’s crust and mantle, but at different speeds; the P waves are always faster than the S waves, but their exact speeds depend on depth and location.

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Bautista, Aldo – Homework 12 – Due: Nov 22 2005, 4:00 am – Inst: Maxim Tsoi 2 For the purpose of this exercise, we assume the P wave’s speed to be v P = 9900 m / s while the S waves travel at a slower speed of v S = 5120 m / s. Suppose a seismic station detects a P wave and then Δ t = 32 . 9 s later detects an S wave. How far away is the earthquake center? Correct answer: 348 . 878 km. Explanation: Suppose the earthquake happens at time t = 0 at some distance d . The P wave and the S wave are both emitted at the same time t = 0, but they arrive at different times, respectively t P = d/v P and t S = d/v S . The S wave is slower, so it arrives later than the P wave, the time difference being Δ t = d v S - d v P = d ( v P - v S ) v P v S .
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Homework 12 - Bautista Aldo Homework 12 Due 4:00 am Inst...

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