# Thread: word problem

1. ## word problem

The period of a simple pendulum is directly proportional to the square root of its length. If a pendulum has a length of 6 feet and a period of 2 seconds, to what lemgth should it be shortened to achieve a 1 second period? My answer is 3 feet but I'm not sure. Thanks for checking this problem.

2. Originally Posted by kwtolley
The period of a simple pendulum is directly proportional to the square root of its length. If a pendulum has a length of 6 feet and a period of 2 seconds, to what lemgth should it be shortened to achieve a 1 second period? My answer is 3 feet but I'm not sure. Thanks for checking this problem.
What we are told may be rewritten as:

$period(length)=k\sqrt{length}$

also:

$period(6)=k\sqrt{6}=2$

so: $k=2/ \sqrt{6}$

Now if the period is 1 s:

$period(length)=2/ \sqrt{6}\times \sqrt{length}=1$

rewriting this gives:

$length=3/2\ ft$

RonL

3. ## answer

Ok I see your answer but I have to chose 1 foot, 1.5 feet, 2 feet, or 3 feet. I guess it is 1.5 feet. thanks for all the help given.

4. Originally Posted by kwtolley
Ok I see your answer but I have to chose 1 foot, 1.5 feet, 2 feet, or 3 feet. I guess it is 1.5 feet. thanks for all the help given.
I think you will find that 3/2=1.5 ft, so yes.

RonL

5. ## answer

Thanks thats what I thought too.