Average angular acceleration back for more

In summary, the CD is rotating at an angular speed of 4.8x10^2 rpm, and at the end of the music it is rotating at 2.1x10^2 rpm. The average angular acceleration of the CD is -0.0069 rad/s^2.
  • #1
nutster
31
0
Hey again. It's that time of week, and once again I'm stumped. There are three problems, but we'll take them one at a time. The first is as follows:

A certain CD has a playing time of 68 minutes. When the music starts, the CD is rotating at an angular speed of 4.8x10^2 revolutions per minute (rpm). At the end of the music, the CD is rotating at 2.1x10^2 rpm. Find the magnitude of the average angular acceleration of the CD. Express your answer in rad/s^2.


What I've tried is to take the difference of the angular displacement (each divided by 60 to change to seconds), multiplied this by 2pi to change to radians, and divide that difference by 68 minutes (4080 seconds). The answer I get is -0.0069 rad/s^2...but this is wrong :uhh:

Here's the 'layout':

((210rpm-480rpm)/60s)*2pi)/(4080s)=-0.0069

What have I done wrong??

Thanks in advance.
 
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  • #2
The only problem is that u have got a wrong sign, otherwise everything else is fine.

-- AI
 
  • #3
Apparently, you did the arithmetic wrong! You analysis looks good but according to my calculator, ((210- 480)/60)(*2 pi)/4080)= -0.01206., not -0.0069.
 
  • #4
Looks OK to me. Why do you think it's wrong?
 
  • #5
Tenali had it correct...the sign was backwards. I'm still not sure why that is, but it was correct. On to my second, relatively unrelated question:

A 65.0 kg person, running horizontally with a velocity of +4.06 m/s, jumps onto a 10.4 kg sled that is initially at rest.
(a) Ignoring the effects of friction during the collision, find the velocity of the sled and person as they move away.

Which I figured out was 3.5 m/s...now my question:

(b) The sled and person coast 30.0 m on level snow before coming to rest. What is the coefficient of kinetic friction between the sled and the snow?

Any suggestions on how to go about solving this?
 
  • #6
Well, if Tenali is right, then the answer is wrong.
The disc is SLOWING DOWN from 480rpm to 210rpm.
 
Last edited:
  • #7
That's what I thought...as the work I did shows. Down with WebAssign! :rofl: Any thoughts on the second problem?
 
  • #8
Better idea...I'll post it to a new thread.
 
  • #9
Honest! i did not set this question!

-- AI
 

1. What is average angular acceleration?

Average angular acceleration is a measure of how quickly an object's angular velocity changes over time. It is calculated by dividing the change in angular velocity by the change in time.

2. How is average angular acceleration different from regular acceleration?

Regular acceleration is a measure of how quickly an object's linear velocity changes over time, while average angular acceleration is a measure of how quickly an object's angular velocity changes over time. They are different because they measure different types of motion.

3. What is the formula for calculating average angular acceleration?

The formula for calculating average angular acceleration is: average angular acceleration (α) = (final angular velocity - initial angular velocity) / time interval.

4. Can average angular acceleration be negative?

Yes, average angular acceleration can be negative. This occurs when an object's angular velocity decreases over time, resulting in a negative value for average angular acceleration.

5. Why is average angular acceleration important?

Average angular acceleration is important because it helps us understand how quickly an object's angular velocity changes, which can provide insights into the object's motion and how forces are acting upon it. It is also a fundamental concept in the study of rotational dynamics and mechanics.

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