Angular Velocity from KE, radius, and mass

  • Thread starter aivilo775
  • Start date
  • #1
aivilo775
5
0
Homework Statement:
A 45-cm-long, 95 g rod rotates about an axle at one end of the rod. At what angular velocity, in rpm , does the rod have 50 mJ of rotational kinetic energy?
Relevant Equations:
Not given
I tried using the equation w^2 = (4*K)/(mr^2) but I don't think this is right... I got my answer to be 3.2243 and that's not correct
 

Answers and Replies

  • #2
SammyS
Staff Emeritus
Science Advisor
Homework Helper
Gold Member
11,693
1,273
Homework Statement::
A 45-cm-long, 95 g rod rotates about an axle at one end of the rod. At what angular velocity, in rpm , does the rod have 50 mJ of rotational kinetic energy?
Relevant Equations:: Not given

I tried using the equation w^2 = (4*K)/(mr^2) but I don't think this is right... I got my answer to be 3.2243 and that's not correct
Hello @aivilo775 ,

:welcome:

Under Relevant Equations, you should supply whatever equations are relevant to your problem, such as: ##KE=(1/2)I\omega^2##
for the problem you posted.

Also of importance is what you use to get the moment of inertia, ##I## .

You need to be more detailed as to how you obtained your result. Also be careful with units and define symbols.
 
  • Like
Likes PhDeezNutz and topsquark
  • #3
aivilo775
5
0
Screen Shot 2022-10-26 at 9.54.32 PM.png

This is the math I did when I rearranged
Screen Shot 2022-10-26 at 9.54.47 PM.png
to solve for w, angular velocity. I used I = mr^2. I got w = 2.27995. The units would be the sqrt of(J /kg*m^2), which ends up just being 1/sec. to get the answer in rpm, I figured I would multiply w by 60sec (to get w = 136.797, but this wasn't right
 
  • #4
kuruman
Science Advisor
Homework Helper
Insights Author
Gold Member
12,596
5,745
Please use LaTeX to write your equations in symbolic form. It is not at all clear what the numbers you posted in #3 are all about. Also, what is the moment of inertia of the rod? Look it up.
 
  • #5
haruspex
Science Advisor
Homework Helper
Insights Author
Gold Member
2022 Award
39,191
8,503

Suggested for: Angular Velocity from KE, radius, and mass

Replies
12
Views
450
  • Last Post
Replies
18
Views
416
  • Last Post
Replies
3
Views
474
  • Last Post
Replies
6
Views
510
  • Last Post
Replies
6
Views
361
Replies
11
Views
564
Replies
14
Views
422
Replies
3
Views
533
Replies
1
Views
386
Replies
6
Views
458
Top