How Long Does It Take for a Flywheel to Reach 125 Rev/Min from Rest?

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Discussion Overview

The discussion revolves around calculating the time taken for a flywheel to reach a speed of 125 revolutions per minute (rev/min) from rest, given that it revolves completely 68 times during this acceleration. The focus is on the application of rotational motion equations and the correct conversion of units.

Discussion Character

  • Homework-related
  • Mathematical reasoning

Main Points Raised

  • One participant presents the problem and initial calculations, noting the given answer of 65.29 seconds.
  • Another participant suggests using the equation of motion for rotation, emphasizing the need to consider uniform acceleration.
  • A third participant reiterates the importance of ensuring angular velocity is expressed in radians per second.
  • A later reply acknowledges a mistake in the calculations and expresses gratitude for the clarification.

Areas of Agreement / Disagreement

Participants generally agree on the need for proper unit conversion and the application of rotational motion equations, but the specific calculations and methods remain unresolved.

Contextual Notes

Limitations include potential missing assumptions regarding the uniform acceleration and the dependence on the correct application of rotational motion equations. The discussion does not resolve the exact method for calculating time.

MMCS
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A flywheel 1.2 m in diameter is uniformly accelerated from rest and revolves completely 68 times in reaching a speed of 125 rev/min. Find the time taken to reach this speed

i have been given the correct answer as 65.29 seconds

Wht i have up to now

ω1 = 0
ω2 = 125 r/min = 125/60 = 2.083 r/s
theta = 68*2∏ = 427.26 rads
t = ?

I have tried to use theta = ((ω1+ω2)*t)/2 rearranged to get t = 2theta/ω1+ω2 however my answer doesn't come close

Any suggestions would be appreciated
 
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you need the equation of motion for rotation. the flywheel is undergoing uniform acceleration; you need to take that into consideration.
 
MMCS said:
ω1 = 0
ω2 = 125 r/min = 125/60 = 2.083 r/s
Make sure ω is in rads/sec.
 
That sorted it, silly mistake, Thanks Doc Al
 

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