Question

A fan at a rock concert is 50.0 m from the stage, and at this point the sound intensity level is 108dB . Sound is detected when a sound wave causes the tympanic membrane (the eardrum) to vibrate . Typically, the diameter of this membrane is about 8.40 mm in humans

How much energy is transferred to her eardrums each second ?

How fast would a 2.00 mg mosquito have to fly to have this much kinetic energy?

How fast a typical 2.0 mg mosquito would have to fly (in mm/s) to have an amount of energy delivered to the eardrum each second when someone whispers (20 dB) a secret in your ear

Answer 1

Please help!

Answer 2

Help please!!!

Answer 3

Help anyone?

Answer 4

Do you remember equation for sound intensity?

Answer 5

Is it 10log(I/10^-12)?

Answer 6

Yes, we call that intensity level (known in the problem). Can you find I (intensity) from than eq?

Answer 7

I got .0631?

Answer 8

Explain your intermediate step?

Answer 9

(108/10)=10.8
10^10.8=6.31
6.31*10^-12=.0631=I

Answer 10

Where did you get 6.31?

Answer 11

To get rid of log, don't you you raise 10 by 10.8?

Answer 12

Yep, correct. Just my habit to make sure everything goes right :)
Now you know I, remember what I is?

Answer 13

.0631

Answer 14

I mean the physical definition or the equation for I

Answer 15

Power/Area

Answer 16

Great, can you find the power of sound that mr rock fan receive?

Answer 17

how do i know the area though?

Answer 18

the area here means the area of sphere located 50 m from the source. Or simply area of sphere with radii 50 m.

Answer 19

I got 31415.93 for the area? If you could stay here, I'd appreciate it. I'll be back in 10-15 minutes.

Answer 20

Yep, now find the power.

Answer 21

1982.21

Answer 22

Find the energy ear receive from this power. You know what power is right?

Answer 23

I have no clue how to find the energy ear from power

Answer 24

you already know P. What is power?

Answer 25

the rate that energy is transferred. not sure on what the equation is

Answer 26

The first question asked is energy ear receive each second. Or the power received by ear.

Answer 27

So, do I have to find the area of the ear and multiply that by I and find that power?

Answer 28

To be clear, the question asked for intensity again, but now only the amount received by ear.
Think like this: the 'sphere' has known power. What is part of power received by some tiiiny area (eardrum's area) of that spehere?

Answer 29

Sorry, but I just don't understand. If you're saying find the power of the ear, I got 1.39*10^-5

Answer 30

It's just the previous I times ear area.

Answer 31

ok, then I got that above your post

Answer 32

Then to mosquito?

Answer 33

I got the answer wrong. The answer is supposed to be in microjoules so I tried converting and ended up with 1.39*10^-11 and it isn't right. Did I do something wrong? I only have two tries left to get this particular question right

Answer 34

I found 3,5 uJ

Answer 35

(for energy transferred)

Answer 36

is that 3.5? the comma threw me off

Answer 37

Sorry, yes, 3.5. in my country, we use 3,5 instead.

Answer 38

Thank You! Could you help me with the mosquito one next?

Answer 39

You are in the right track, just miscalculated i guess.
For the mosquito, remember the equation for kinetic energy?
If you do, the kinetic energy must be equal to 3,5 uJ.

Answer 40

in uJ or just Joules?

Answer 41

Whichever you want, just dont forget to equate the unit.

Answer 42

Can anyone help me with this second question?

Answer 43

kinetic energy = 1/2mv^2 correct? Because I'm not sure if i'm getting the right answer

Answer 44

K=1/2 m v^2 right. This K must be equal to your 3,5 uJ :)

Answer 45

ok, got it. so the third question?

Answer 46

Just redo the whole problew with that new intensity.

Answer 47

I got 886.23 but got it wrong?

Answer 48

For the power received by ear, just multiply 20dB with ear area. Make sure the units are correct. Do this once again, i'm sorry. I have to sleep now, already 2 am here.

Answer 49

Ok, I keep getting the third question wrong. Can someone help me?

Answer 50

What's your last answer for third question.

Answer 51

I had .1489

Answer 52

What is the intensity with 20dB intensity level?

Answer 53

1*10^-10

Answer 54

Unit?

Answer 55

W/m^2

Answer 56

Okay, now multiply this with ear area in m^2

Answer 57

I got 2.217*10^-14, is that correct so far?

Answer 58

I found 5,541 x 10^-15. Area of eardrum in m^2=?

Answer 59

For the area of the eardrum I got 4pi(.0042^2)=2.2167*10^-4. Is my formula right?

Answer 60

I got 5,542 x 10^-5 m^2 for area. "4pi"?

Answer 61

Are we calculating the area of a sphere? or is it supposed to be a circle?

Answer 62

It's a circle I guess.

Answer 63

Oh, okay then. So, then I would calculate power and end up with 5.542*10^-15

Answer 64

Yes, that's energy in one scond. The unit's still Joule, to keep our track of unit in SI. Now find the speed of mosquito

Answer 65

I got 7.44*10^-5 m/s. How would I get this to mm/s?

Answer 66

You remember to use kg for mass?

Answer 67

yes, I did that. 2*10^-6 for the mosquito's mass

Answer 68

Okay, to convert to mm/s, just multiply with 10^3

Answer 69

Thanks! I have a fourth question for this problem and it says "Compare the mosquito's speeds found in parts B and C" and then it says "Please enter your number (factor) without the units." I have no idea what this is asking.

Answer 70

it means vb/vc
Dont forget to make the units same first.

Answer 71

Thanks so much for your help. Would it be ok with you if I asked a couple more open questions. I have one chance left to get those right and I feel like I did them right

Answer 72

Yes, i'd like to help. But i have like 15 minutes. Have to do something else :)