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I am trying to do a simple pendulum problem but for some reason my answer is different from the book's answer and I don't know what I am doing incorrectly.

The question is:

Consider a simple pendulum that has a length of $50$cm and a maximum horizontal displacement of $8$ cm.

The first portion asks to find the period. So period of a pendulum can be calculated as $T=2\pi \sqrt{\frac{l}{g}}$ where $l$ is the length and $g$ is gravity = $9.81$. Therefore, period of my pendulum should be:

$$\begin{align} &T=2\pi \sqrt{\frac{l}{g}} \\ &T=2\pi \sqrt{\frac{50}{9.81}}\\ &T=14.185 \end{align}$$

But the back of the is suggesting that answer is $T=1.412$s

What am I doing wrong?

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I think you are mixing units --- that figure for $g$ is in meters, but your lengths are in centimeters. –  Gerry Myerson Apr 14 '13 at 12:34
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1 Answer

up vote 1 down vote accepted

Units! The $l=50$ is for 50 cm, but $g=9.81 m/s^2$ (meters per second second). So you should convert them to the same units before you divide, say write $l=0.5 m$.

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What a silly mistake! Thanks! –  gekkostate Apr 14 '13 at 13:01
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