Flywheel Rotation Question

  • Thread starter Arman777
  • Start date
  • #1
1,872
147

Homework Statement


A flywheel turns through 40 rev as it slows from an angular speed of 1.5 rad/s to a stop.Assuming a constant acceleration,find the tme for it to come to rest.

Homework Equations


##w-w_0=∝t##

The Attempt at a Solution


In Δt secon the change in w will be 1.5 and this time it will rotate 40 times..I tried every equaiton like
0-1.5=∝t
or
40=1.5t-1/2∝t^2
but I couldnt found
 

Answers and Replies

  • #2
686
172
40=1.5t-1/2∝t^2
but I couldnt found
There is another equation that you should know that involves initial and final velocities, acceleration and angle of rotation.
Also, you are mixing units here: revolutions and radians.
 
  • #3
BvU
Science Advisor
Homework Helper
13,880
3,432
Check the units of your last equation (I wonder: why couldn't you solve it ? - or did it just give the wrong answer ?)
 
  • #4
1,872
147
Check the units of your last equation (I wonder: why couldn't you solve it ? - or did it just give the wrong answer ?)
I am really bad at this whole rotation-torque subject.I ll look again..I know my equation is wrong...
 
  • #5
ehild
Homework Helper
15,543
1,909
What is the turning angle when the flywheel rotates 40 times?
Also check the signs.
 
  • #7
ehild
Homework Helper
15,543
1,909
turning angle ?
Or angle of rotation. What is the angle the wheel rotates during one revolution?
 
  • #10
ehild
Homework Helper
15,543
1,909
  • #12
ehild
Homework Helper
15,543
1,909
I posted 80π ?
Yes. So what are the equations for the change of angular velocity and angular rotation angle in time Δt?
 
  • #13
1,872
147
##w-w_0=∝t##and
##Δθ=wt ##

or ##Δθ=wt-\frac 1 2∝t^2##
 
  • #14
ehild
Homework Helper
15,543
1,909
##w-w_0=∝t##and
##Δθ=wt ##

or ##Δθ=wt-\frac 1 2∝t^2##
Δθ=wt is only valid for constant angular velocity.
##Δθ=w_0t+\frac {1 }{2}\alpha t^2## that is valid with positive sign.
Eliminate alpha.
 
Last edited:
  • #15
1,872
147
I guess I have to study this more to understand the basics.I ll open another thread
 
  • #17
1,872
147
Δw=-1.5 and Δθ is 80 so

Δw=-1.5=∝t and

80=1.5t-1/21.5t

Is this true ?
 
  • #18
686
172
The rotational equations pretty much follow directly from the linear equations. So if you can remember the linear equations, the rotational should be easy.
v = vo + at → ω = ωo + αt
v2 = vo2 + 2ax → ω2 = ωo2 + 2αθ
x = vot + at2/2 → θ = ωot + αt2/2
F = ma → Γ = Iα
ρ = mv → L = Iω
Ek = mv2/2 → Ek = Iω2/2

80=1.5t-1/21.5t

Is this true ?
I think so, except it should be 80π instead of 80.
 
  • Like
Likes Arman777
  • #19
1,872
147
Ok,I found....Thanks all of you...Just couldnt see that
 
  • Like
Likes TomHart

Related Threads on Flywheel Rotation Question

  • Last Post
Replies
10
Views
580
  • Last Post
Replies
3
Views
168
  • Last Post
Replies
2
Views
2K
Replies
4
Views
947
  • Last Post
Replies
4
Views
1K
  • Last Post
Replies
3
Views
4K
  • Last Post
Replies
1
Views
3K
  • Last Post
Replies
2
Views
2K
Replies
1
Views
2K
Replies
1
Views
7K
Top