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Inga [223]
4 years ago
10

A swimmer can swim at a velocity v in still water. She swims upstream a distance d against the current, which has a velocity u.

She then swims back to her starting point. A) how long does it take her to make the round-trip? B) what is her average speed for the trip? C) for what value of u u is her average speed the greatest?
Physics
1 answer:
xxTIMURxx [149]4 years ago
4 0
Upstream speed: v - u
Downstream speed: v + u
Total distance: 2d

A) total time = d / (v - u)  + d / (v + u)

B) Average speed = total distance / total time
V(av) = 2d / [ d / (v -  u) + d / (v + u) ]
V(av) = 2d / [d(v + u + v - u) / (v - u)(v + u) ]
V(av) = (v² - u²) / v

C) If u is 0, her average speed will be the greatest, equal to v
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2 years ago
One of the harmonic frequencies of tube A with two open ends is 576 Hz. The next-highest harmonic frequency is 648 Hz. (a) What
balu736 [363]

(a) 288 Hz

The difference between any two harmonics of an open-end tube is equal to the fundamental frequency, f_1 (first harmonic):

f_{n+1}-f_n = f_1 (1)

In this problem, we are told the frequencies of two successive harmonics:

f_n = 576 Hz\\f_{n+1}=648 Hz

So the fundamental frequency is:

f_1 = 648 Hz-576 Hz=72 Hz

Now we know that one of the the harmonics is f_n=216 Hz, so its next highest harmonic will have a frequency of

f_{n+1}=f_n+f_1 = 216 Hz+72 Hz=288 Hz

(b) n=4

The frequency of the nth-harmonic is an integer multiple of the fundamental frequency:

f_n=n f_1 (2)

Since we know f_n = 288 Hz, we can solve (2) to find the number n of this harmonic:

n=\frac{f_n}{f_1}=\frac{288 Hz}{72 Hz}=4

(c) 4445 Hz

For a closed pipe (only one end is open), the situation is a bit different, because only odd harmonics are allowed. This means that the frequency of the nth-harmonic is an odd-integer multiple of the fundamental frequency:

f_n=(2n+1) f_1 (2)

so, the difference between any two harmonics tube is equal to:

f_{n+1}-f_n = (2(n+1)+1)f_1-(2n+1)f_1=(2n+3)f_1-(2n+1)f_1=2f_1 (1)

In this problem, we are told the frequencies of two successive harmonics:

f_n = 4699 Hz\\f_{n+1}=4953 Hz

So, according to (1), the fundamental frequency is equal to half of this difference:

f_1 = \frac{4953 Hz-4699 Hz}{2}=127 Hz

Now we know that one of the harmonics is f_n=4191 Hz, so its next highest harmonic will have a frequency of

f_{n+1}=f_n+2f_1 = 4191 Hz+254 Hz=4445 Hz

(d) n=17

We said that the frequency of the nth-harmonic is equal to an odd-integer multiple of the fundamental frequency:

f_n=(2n+1) f_1 (2)

Since we know f_n = 4445 Hz, we can solve (2) to find the number n of this harmonic:

n=\frac{1}{2}(\frac{f_n}{f_1}-1)=\frac{1}{2}(\frac{4445 Hz}{127 Hz}-1)=17

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3 years ago
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