• Support PF! Buy your school textbooks, materials and every day products Here!

Something weird about Rotational Kinematic Equations

  • Thread starter Stefenng
  • Start date
  • #1
10
0

Homework Statement


I need to find the average acceleration of a gramophone record.

Initial angular velocity, W = 0
Final angular velocity, w = 3.50rad s^-1
angular displacement, 8 = 0.25rad

Homework Equations


The equation given by the answer is

t= 8/w
a = ( w - W ) / t
the answer is 49.0 rad s-2


The Attempt at a Solution


This is the equation I use

w2 = W2 + 2a8

and I get 24.5rad s-2

But if I multiply it with 2, the angular acceleration will become 49rad s-2

That mean my equation will become
w2 = W2 + a8

Can anyone explain this to me?
Or I use a wrong equation?
 

Answers and Replies

  • #2
181
0

Homework Equations


The equation given by the answer is

t= 8/w
a = ( w - W ) / t
the answer is 49.0 rad s-2


The Attempt at a Solution


This is the equation I use

w2 = W2 + 2a8

and I get 24.5rad s-2
You are right:

t= 8/w is wrong because the angular velocity is not constant

It should be t= 28/w
 
  • #3
10
0
ok...thx... ^^
 
  • #5
tiny-tim
Science Advisor
Homework Helper
25,832
249
Last edited by a moderator:

Related Threads for: Something weird about Rotational Kinematic Equations

Replies
3
Views
1K
Replies
12
Views
237
  • Last Post
Replies
4
Views
3K
  • Last Post
Replies
2
Views
12K
  • Last Post
Replies
1
Views
1K
  • Last Post
Replies
2
Views
1K
  • Last Post
Replies
2
Views
506
  • Last Post
Replies
10
Views
2K
Top