Vagabond7
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Edit: Nevermind, solved it.
A ceiling fan with 80 cm-diameter blades is turning at 60rpm . Suppose the fan coasts to a stop 25 s after being turned off.
What is the speed of the tip of the blade 10 seconds after being turned off?
Through how many revolutions does the fan turn while stopping?
It's just kinematic stuff, just rotational, no particularly complex equations.
Ok, so the first part I could solve just fine.
I solved for the rotational acceleration using Vf=Vi+at where Vf=0, Vi=pi*.8=2.51 m/s(thanks to the easy conversion of 60rpm to m/s) and t=25s. The acceleration was -.1004. Then I just replugged the values in and solved for Vf at 10 seconds getting 1.5 m/s. That went fine, it was the correct answer.
The second part is where I am getting trouble. I figured I could just use a general kinematic displacement equation like df=di+vt+.5at^2 to get the distance traveled and then just divide by the circumference...which now that I am typing, I am realizing I put the wrong thing in my calculator, and I just solved it. Lolz. I divided by 2*pi*.8, but .8 is the diameter not the radius. pi*.8 gets me the right answer.
*sigh,* don't you hate it when you get caught up, not by a lack of understanding, but by just dumb errors? Well thanks for the speedy replies I know I would've gotten. I'll probably be back for more help later.
Homework Statement
A ceiling fan with 80 cm-diameter blades is turning at 60rpm . Suppose the fan coasts to a stop 25 s after being turned off.
What is the speed of the tip of the blade 10 seconds after being turned off?
Through how many revolutions does the fan turn while stopping?
Homework Equations
It's just kinematic stuff, just rotational, no particularly complex equations.
The Attempt at a Solution
Ok, so the first part I could solve just fine.
I solved for the rotational acceleration using Vf=Vi+at where Vf=0, Vi=pi*.8=2.51 m/s(thanks to the easy conversion of 60rpm to m/s) and t=25s. The acceleration was -.1004. Then I just replugged the values in and solved for Vf at 10 seconds getting 1.5 m/s. That went fine, it was the correct answer.
The second part is where I am getting trouble. I figured I could just use a general kinematic displacement equation like df=di+vt+.5at^2 to get the distance traveled and then just divide by the circumference...which now that I am typing, I am realizing I put the wrong thing in my calculator, and I just solved it. Lolz. I divided by 2*pi*.8, but .8 is the diameter not the radius. pi*.8 gets me the right answer.
*sigh,* don't you hate it when you get caught up, not by a lack of understanding, but by just dumb errors? Well thanks for the speedy replies I know I would've gotten. I'll probably be back for more help later.