Finding time in circular motion

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Homework Help Overview

The problem involves calculating the time it takes for the blades of a food blender to complete one revolution, given their speed and the radius of the circular path. The subject area pertains to circular motion and kinematics.

Discussion Character

  • Exploratory, Assumption checking, Mathematical reasoning

Approaches and Questions Raised

  • Participants discuss the correct formula for calculating the period of rotation and question the validity of the original equation used. There are attempts to derive the period from the given speed and radius, and some participants express confusion over their results.

Discussion Status

The discussion is ongoing with various approaches being explored. Some participants have provided alternative methods for calculating the period, while others are questioning the assumptions made about the speed and the equations used. There is no clear consensus on the correct answer yet.

Contextual Notes

Participants note potential issues with the given speed value and its interpretation, suggesting that there may be a misunderstanding regarding the units or context of the problem. There is also mention of a possible error in the original problem statement.

tyro008
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Homework Statement


The tips of the blades in a food blender are moving with a speed of 15 m/s in a circle that has a radius of 0.052m. How much time does it take for the blades to make on revolution?


Homework Equations


T=(2XpiXr)/T
T: period of time it takes to complete one cycle

The Attempt at a Solution


I tried using the equation under "relevant equations" and got 0.02seconds as an answer. This is wrong but I don't know what other equation to use..
 
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Your equation is all wrong. Its T = 2*pi*r / velocity
 
oh whoops. but.. i tried that and it still didn't work..
is there another equation that i should use instead?
i feel that my T represents time, but not the one I'm looking for
 
Lets break it down. r = 0.052 meters. The circumference is 2 pi 0.052 which is 0.104 pi meters. It rotates at velocity 15 meters every second. So this means that it does 15/0.104 pi revolutions every second. Then just inverse that quantity to find how many seconds is one revolution
 
i keep getting 0.02 seconds, but this isn't the right answer.
is this what you got, too?
 
V^2/r= 4 pi^2 r/T^2

solve for T

EDIT: Forgot square T
 
Last edited:
tyro008 said:
i keep getting 0.02 seconds, but this isn't the right answer.
is this what you got, too?

If there is another answer other than 0.02 seconds then that answer has to be wrong. Only thing else I can think of is if you got 15 m/s wrong and it was supposed to be 15 radians per second.
 
Epsillon said:
V^2/r= 4 pi^2 r/T

solve for T

Epsillon what is this equation?? this basically says v =[tex]\frac{2\pi}{ \sqrt{T}}[/tex]
 
Oh sorry I forgot to square the T (silly mistake)

its 4pi^2r/T^2
 
  • #10
Epsillon said:
Oh sorry I forgot to square the T (silly mistake)

its 4pi^2r/T^2

Ok it still gives v = [tex]\frac{2 \pi}{T}[/tex] which gives him the "wrong" answer. Obviously which ever book or person giving the answer is wrong.
 
  • #11
haha, thanks anyways you guys.
you know, i think you guys are right. i'll talk to my teacher about changing the answer :)
 

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