tbr cbt question

[cloak25]

If τ of a membrane with a fundamental frequency of 125 Hz is increased by ∆τ, then the membrane’s fundamental frequency is increased by:

​

By what percent should τ be increased in order to raise the fundamental frequency to 131 Hz?

A. 0.1%
B. 5%
C. 10%
D. 100%

The explanation to this question was kind of confusing so if anyone can post their reasoning, i'd appreciate it thanks.

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[Jepstein30]

If τ of a membrane with a fundamental frequency of 125 Hz is increased by ∆τ, then the membrane’s fundamental frequency is increased by:

​

By what percent should τ be increased in order to raise the fundamental frequency to 131 Hz?

A. 0.1%
B. 5%
C. 10%
D. 100%

The explanation to this question was kind of confusing so if anyone can post their reasoning, i'd appreciate it thanks.

6 = .5(X)125 where X is deltaT/T

12/125 is just under .1 so .1 = deltaT/T

Now, example being if T was 100:

.1 = deltaT/100

100 * .1 = deltaT = 10

DeltaT is 10. 10/100 is 10%.

I think that should be right, is the answer C?

 

[cloak25]

yes you're right its C. Yea, the explanation made it more complicated than it is. I forgot that the deltaF term is change in frequency so it should be 6...so it's basically a plug and chug question. damn. thanks alot, glad it's cleared up now!

 

[Jepstein30]

yes you're right its C. Yea, the explanation made it more complicated than it is. I forgot that the deltaF term is change in frequency so it should be 6...so it's basically a plug and chug question. damn. thanks alot, glad it's cleared up now!

Yea, to be honest, I usually don't go with the any of the book's methods to get these type of answers quickly. I'm pretty fast doing quick math accurately and would much rather do the work and make sure i have it right than think about the problem and find some trick.

I've found that most of these harder plug and chugs can be solved the same way SAT problems can be.. plug in easy numbers of your own.