Question

物理题求助！！！关于波的，很简单，不过是英语的~~

1。A source of sound waves of frequency 1.0 kHz is traveling through the air at 0.50 times the speed of sound. (a) Find the frequency of the sound received by a stationary observer if the source moves towards her. (b) Repeat if the source moves away from her instead.

(a) 5.0 kHz; (b) 679 Hz
(a) 2.0 kHz; (b) 667 Hz
(a) 7.0 kHz; (b) 677 Hz
(a) 2.0 kHz; (b) 677 Hz
(a) 5.0 kHz; (b) 667 Hz
2。An air bubble ascends from the bottom of a lake 9.2 m deep. The temperature at the bottom of the lake is 8 C, and near the surface it is 25 C. How many times larger in volume is the bubble at the top of the lake compared with its volume at the bottom?

3。You place 3.7 g of water at room temperature in a pressure cooker (a sealed pot) of volume 2.7 L and heat the water to 204 C. What is the pressure in the cooker?
4.The pitch of the sound from a racecar engine drops the musical interval of a fourth when it passes the spectators. This means the frequency of the sound after passing is 0.75 times what it was before. How fast is the racecar moving?
5.Find the mass (in kg) of one molecule of CO2.

7.31 10-26 kg
7.31 10-23 kg
7.38 10-26 kg
7.38 10-23 kg

6.The pitch of the sound from a racecar engine drops the musical interval of a fourth when it passes the spectators. This means the frequency of the sound after passing is 0.75 times what it was before. How fast is the racecar moving?

49 m/s
61 m/s
68 m/s
72 m/s

7.An ideal gas that occupies 1.8 m3 at a pressure of 1.0 ?105 Pa and a temperature of 27 C is compressed to a volume of 0.8 m3 and heated to a temperature of 228 C. What is the new pressure? Pa

Answer 1

1。设声源相对媒质的运动速度为v观察者相对媒质的速度为u，媒质中的声速为c,声源的振动频率与观察者接收到的频率分别为f0与f，多普勒效应公式的一般表达式为
（1）相对运动 f=(c+u)/(c-v)*fo
（2）背离运动 f=(c-u)/(c+v)*fo
v=170 m/s c=340 m/s u=0
(a) f=340/(340-170)*1.0=2.0 (kHz)
(b) f=340/(340+170)*1.0=0.667（kHz)=667Hz

抱歉，先答一题………………有时间再答其余两个（话说不学物理已经很多年……）