a few questions on waves (EK physics)

[astronaut135]

644. A transverse wave travels along a perfectly elastic string parallel to the ground. Any given point on the string:

a) doesn't move
b) moves up and down
c) moves up only
d) moves left and right

I know that a transverse waves has a displacement perpendicular to direction of propagation. Wouldn't both (b) and (d) fit this description? The book says that (b) is the correct answer, can anyone explain this?

677. An increase in which of the following properties of gas by itself, will decrease the speed of sound through the gas?

a) pressure
b) density
c) temperature
d) volume

Not sure how to reason through this question. However, the book says that (b), an increase in density would decrease the speed of sound. But doesn't sound travel faster than water, which is more dense than air?

Thanks in advance!

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[The Kraken]

644. A transverse wave travels along a perfectly elastic string parallel to the ground. Any given point on the string:

a) doesn't move
b) moves up and down
c) moves up only
d) moves left and right

I know that a transverse waves has a displacement perpendicular to direction of propagation. Wouldn't both (b) and (d) fit this description? The book says that (b) is the correct answer, can anyone explain this?

Imagine you're in a wave pool. If you are floating in an inner tube (beer in your hand I hope), you just move up and down, not around.

 

[The Kraken]

677. An increase in which of the following properties of gas by itself, will decrease the speed of sound through the gas?

a) pressure
b) density
c) temperature
d) volume

Not sure how to reason through this question. However, the book says that (b), an increase in density would decrease the speed of sound. But doesn't sound travel faster than water, which is more dense than air?

Thanks in advance!

The question says "properties of gas by itself". You can't switch to a liquid or solid to logic through this question.

speed of sound in a media = (gamma*pressure/density)^.5

Write it out on a piece of paper, makes this easier. The gamma is not important to this question. So in the numerator you have pressure. Increasing pressure = increase speed of sound, not right, so not A. Density is in the denominator, increasing the denominator = lowering speed of sound, making B correct.

 

[The_Sunny_Doc]

Imagine you're in a wave pool. If you are floating in an inner tube (beer in your hand I hope), you just move up and down, not around.

LOL! Great explanation. 👍 Thanks for the bit of humor during this agonizing final stretch of cramming.