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AP Physics B 1.1 Waves and Optics
185 Views

AP Physics B: Waves and Optics Drill 1, Problem 1. Which of the following is technically true for Max as he stands still at the edge of oblivion?

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AP Physics B 1.1 Waves and Optics 185 Views


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AP Physics B: Waves and Optics Drill 1, Problem 1. Which of the following is technically true for Max as he stands still at the edge of oblivion?

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Transcript

00:03

Here's your shmoop du jour, brought to you by the Grand Canyon.

00:07

Almost as awe-inspiring as AP Physics.

00:10

Max is scolded by his parents for leaning over the railing of a dangerous vista at the Grand Canyon.

00:15

Mom conveys her distress as she steps back from the ledge,

00:18

and Dad cries out while lunging forward to grab his son. 

00:21

Which of the following is technically true for Max

00:23

as he stands still at the edge of oblivion?

00:26

You know... other than the fact that he now has proof his parents love him?

00:30

And here are the potential answers...

00:36

This problem doesn't have a lot of numbers, so it's clearly a conceptual one.

00:39

Heck, there are no numbers at all. If we glance at the answers,

00:42

we'll see that they all have to do with the perceived pitch of Max's parents' cries.

00:47

Also, the problem give us information on the motion of his parents.

00:51

When we have waves and movement, our mind should immediately snap to the Doppler effect.

01:01

Named for Christian Doppler, it's the phenomenon that occurs when a source of waves is in motion.

01:06

Say, for example, that we had a speaker emitting a tone with a frequency of 100hertz.

01:12

A listener 1 meter away would hear a frequency of 100 hertz.

01:16

A listener 2 meters away would hear the same frequency.

01:20

No matter how far, the sound is still 100 hertz.

01:23

But, uh... what the heck is a hertz?

01:26

A hertz is a measurement of one cycle of sound per second.

01:30

One hertz every second the sound wave oscillates - moves up and down - one time.

01:36

If a sound has a frequency of 100 hertz, it oscillates 100 times in a second.

01:44

This rate of oscillation determines how high or low a sound is.

01:47

A higher frequency means a higher sound.

01:50

What if the speaker starts moving?

01:52

If the speaker moves away from the listeners, then the distance between each wave would increase.

02:02

This decreases the frequency and creates a lower tone.

02:06

On the other hand, if the speaker moves toward the listeners,

02:09

the waves would become closer together, and a higher tone would be heard.

02:17

So Max's father moving toward him will sound higher, and his mother will sound lower.

02:22

The only answer that fits this description is (D).

02:26

Next year's family vacation?

02:28

Kansas.

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