<p>if a pendulum is swinging, and the measure of the angle is 2.5 radians, and the measure of the arc is 50 centimeters, what is the length of the pendulum in centimeters?
i had no idea how to do this so i just did:
2.5x=50
x=20
is that correct?
(this was a math b regents question btw today)</p>
<p>Anyone correct me if I'm wrong.</p>
<p>2.5 radian = 2.5 x 180/pi = 143.24
143.24/360 = .397888
^^ that would be the percent 143.24 degree or 50 cm would be of the whole circle.
so .397888 x 2pi(r) [circumference] = 50
r = 20</p>
<p>Uh I hope..</p>
<p>i said 2.5x=50
i got 20, i don't know if i'll get all the points for the work though :/</p>
<p>I think what you did is fine. Since the pendulum swings in an arc, s=r*theta can be used - and the length of the pendulum is the "radius".</p>
<p>i feel like i should have added an equation like radiansxradius=arc, but i didn't.
What did you guys think of the proof?</p>
<p>oh, do you any of you remember the numbers for the last question from the multiple choice? the one that the angle was 60 degrees; side opposite was __ and on of the other side was __</p>
<p>"2.5 radian = 2.5 x 180/pi = 143.24
143.24/360 = .397888
^^ that would be the percent 143.24 degree or 50 cm would be of the whole circle.
so .397888 x 2pi(r) [circumference] = 50
r = 20
"</p>
<p>all that work is really unnecessary.
You can just do</p>
<p>2pi*r/2pi=50/2.5
which will be r=20</p>