TUTORIAL ANSWERS 442-448

 

 

 
 

Your Answer to Q442.  Sorry, your answer is not correct. Did you remember to convert mass to weight?

Help: Fundamentals of Sound, Sec. 10-A.

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Hint for Question 442:  A one kilogram mass weighs 10 Newtons on Earth.
 

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Your Answer to Q442. Congratulations, your answer is correct.

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Correct Answer to Question 442: The force exerted is 100 Newtons since each kilogram weighs 10 Newtons on Earth. The distance through which the force is exerted is the vertical height of the stairs, that is, 6 m so the work done is 100x6 = 600 Joules or answer b).

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Your Answer to Q444.  Sorry, your answer is not correct.

Help: Fundamentals of Sound, Sec. 10-F.

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Hint for Question 444: Brightness depends on power not energy. Power is energy per second.
 

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Your Answer to Q444 . Congratulations, your answer is correct.

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Correct Answer to Question 444: Brightness depends on power, not just energy. Power is energy per second. So bulb A burns with a power of 100 J/5 s = 20 Watts, B with a power of 50/2 = 25 Watts. Note that B has burned less total energy, but has used its energy at a faster rate. The correct answer is b).

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Your Answer to Q445.  Sorry, your answer is not correct.

The correct answer is here.

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Correct Answer to Question 445: c) Three. While one physicist screws in the bulb, the other two argue over which equations to use.

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Your Answer to Q446.  Sorry, your answer is not correct.  Brightness depends on intensity.

Help: Fundamentals of Sound, Sec. 10-G.

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Hint for Question 446: Brightness depends on intensity; intensity is power per unit area (Watts per square meter.)
 

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Your Answer to Q446. Congratulations, your answer is correct.

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Correct Answer to Question 446: Brightness depends on intensity; intensity is power per unit area (Watts per square meter or Watts per square centimeter). Thus the intensity of lightbulb A is 20 W/2 cm2 = 10 W/cm2. Lightbulb B's intensity is 25/5= 5 W/cm2. So now it is lightbulb A which shows the brighter spot and answer a) is correct.

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Your Answer to Q448.  Sorry, your answer is not correct. How does intensity depend on amplitude?

Help: Fundamentals of Sound, Sec. 10-G.

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Hint for Question 448: Intensity depends on amplitude squared, that is, if you double the amplitude the intensity goes up by 4 not 2. 

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Your Answer to Q448. Congratulations, your answer is correct.

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Correct Answer to Question 448:  Intensity increases like the square of amplitude, or I = I0(A/A0)2. Here I0 = 6 picowatts/m2 and A/A0 = 3. Thus I = 6(3)2 = 6x9 = 54 picowatts/m2. The correct answer is b). [A picowatt is a small fraction of a Watt, namely 10-12 Watt.]

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