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# Waves question Watch

1. A recording station observed that there was an interval of 68s between the reception of P (push or primary) waves and S (shake or secondary waves) from an underground nuclear test explosion.
The speed of P and S waves in the Earths crust are 7800 ms^-1 and 4200 ms^-1, respectively.

Calculate the distance of the test site from the explosion

2. Use a modified s = vt
Tell me if you need more detail.
3. Speed P * (Time S - 68) = Speed S * Time S

Find Time S with this equation, and then use distance = speed x time for S.
4. (Original post by morgan8002)
Use a modified s = vt
Tell me if you need more detail.
we dont know the time for the individual waves, just the difference is 68..

so v= s x (t-68) ?
5. (Original post by tjthedj)
we dont know the time for the individual waves, just the difference is 68..

so v= s x (t-68) ?
As the post above said, you can create two s = vt equations and equate them.

6. (Original post by tjthedj)
we dont know the time for the individual waves, just the difference is 68..

so v= s x (t-68) ?
I just told you how to do it.

The difference is 68 seconds

So Time(1) = Time(2)-68

They travel the same distance, so in the equation s=vt, we have vt=vt

Speed (1) * Time(2)-68 = Speed (2) * Time (2)

Solve for Time (2).
7. (Original post by Kolasinac138)
I just told you how to do it.

The difference is 68 seconds

So Time(1) = Time(2)-68

They travel the same distance, so in the equation s=vt, we have vt=vt

Speed (1) * Time(2)-68 = Speed (2) * Time (2)

Solve for Time (2).

sorry completely missed this! i get it now, thanks so much

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Updated: January 13, 2015
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