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

Rotational Kinematics

  • Thread starter nautica
  • Start date

nautica

A phonograph record slows from an initial 45 rpm at a rate of .05 rad/s^2.

a) how long does it take to come to rest???

orig rotational velocity = 45 rpm = 4.71 rad/sec
acc = -.05 rad/s^2

0 = 4.71 rad/s + (-.050 rad/s^2) t
t = 94.2 s

b) How many revolutions does it make before stopping???

(w + w)/2 = (4.71 rad/sec)/2 = 2.355 rad/s * 94.2 s = 221.84 rads =
35.31 rev

Last one for the week. How does this look???

Thanks agaiin
Nautica
 
512
0
I think it's correct.

Here's a shorter and more precise way to do (b):

Without slowing down, you get
45*94.2/60 = 70.65 revolutions.
When slowing down, you know the answer is half of that:
35.325 revolutions.
 

nautica

Thanks, but for some reason the longer version makes more sense to me.

Nautica
 

Related Threads for: Rotational Kinematics

  • Posted
Replies
10
Views
2K
  • Posted
Replies
1
Views
1K
  • Posted
Replies
2
Views
468
  • Posted
Replies
2
Views
1K
  • Posted
Replies
1
Views
2K
  • Posted
Replies
1
Views
3K
  • Posted
Replies
22
Views
2K
  • Posted
Replies
3
Views
1K

Physics Forums Values

We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling
We Value Civility
• Positive and compassionate attitudes
• Patience while debating
We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving
Top