Physics Exam

2007-01-05 11:28 pm

Jane has a mass of 50 kilograms. Express her mass in grams and hectograms.
a. 50,000 g; 5,000 hg.
b. 500,000 g; 500 hg.
c. 500,000 g; 5,000 hg.
d. 50,000 g; 500 hg.
By what amount does the intensity level decrease when you triple your distance from a source of sound?
a. 9.5 dB
b. 4.8 dB
c. 6.0 dB
d. 3.0 dB

回答 (2)

魏王將張遼

2007-01-06 12:25 am

✔ 最佳答案

1) Since 1 kilo = 1000 and 1 kilo = 10 hecto (1 hecto = 100)

Thus multiplying the units accordingly:
50 kilograms = 50,000 grams
50 kilograms = 500 hectograms

Therefore, the answer is D.

2) Assuming the power of the sources remains unchanged. Surface area is 9 times as large as before when the distance is tripled.

So to speak, the intensity is only 1/9 of before after tripling the distance since intensity is inversely proportional to the surface area.

Hence, let the original intensity be I, then new intensity = I/9
New intensity level = 10log(I/9)
= 10log I - 10log 9
= 10log I - 9.5

which is 9.5 dB less than the original intensity level.

Therefore, the answer is A.

參考: My Physics knowledge

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用戶6488

2007-01-05 11:33 pm

1a
2a

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