WEBVTT

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This is Giancoli Answers
with Mr. Dychko.

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The speed of his transverse
wave on a cord

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equals the square root
of the tension in the cord

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divided by its mass
per unit length,

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<i>μ</i> can be replaced
by mass divided by length

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and multiply top and bottom
by <i>l</i>

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and the <i>l's</i> cancel on the bottom,
leaving us with tension force

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times <i>l</i> over <i>m</i>
all square rooted is the speed.

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And that's useful because
the time it takes to go from one

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end of the court to the other
is going to be the length of the court

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divided by that speed.

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And so we have <i>l</i> multiplied
by the reciprocal of this

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instead of dividing by it,
we'll multiply it by its reciprocal.

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So, we have <i>l</i> times
square root <i>m</i> over <i>FT l</i>.

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And this works out
to square root <i>m l</i> over <i>FT</i>

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because the <i>l</i>
divided by square root <i>l</i>

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becomes just square root <i>l</i>

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which we can then put underneath
the square root sign if we like.

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So, square both sides

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and you get <i>t</i> squared
is <i>ml</i> over <i>FT</i>.

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And then multiply both sides
by <i>FT</i> over <i>t</i> squared.

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And end up with tension forces
<i>ml</i> over <i>t</i> squared

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and that's 0.4 kilograms times 8.7 meters
divided by 0.85 seconds squared

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which is 4.8 newtons of tension.