How many revolutions per minute is the sample making

  • Thread starter Thread starter Serena_Greene
  • Start date Start date
  • Tags Tags
    Per Revolutions
Click For Summary
SUMMARY

The discussion revolves around calculating the revolutions per minute (rpm) of a centrifuge sample based on its centripetal acceleration. The centripetal acceleration is given as 8.75 x 10^3 times the acceleration due to gravity, leading to an incorrect calculation of 155 m/s for the acceleration. The correct acceleration should be approximately 86,000 m/s². The user mistakenly converted the velocity to meters per hour instead of meters per minute, which contributed to the incorrect final answer of 5284 rpm.

PREREQUISITES
  • Understanding of centripetal acceleration and its calculation
  • Familiarity with unit conversions, particularly between m/s and m/min
  • Basic knowledge of rotational motion and angular velocity
  • Proficiency in using the formula a = ω²r for angular motion
NEXT STEPS
  • Review the calculation of centripetal acceleration using a = 8.75 x 10^3 * 9.8 m/s²
  • Learn about converting units from m/s to m/min for rotational speed calculations
  • Study the relationship between angular velocity (ω) and revolutions per minute (rpm)
  • Practice problems involving the formula a = ω²r to solidify understanding of rotational dynamics
USEFUL FOR

Students studying physics, particularly those focusing on mechanics and rotational motion, as well as educators looking for examples of common calculation errors in physics problems.

Serena_Greene
Messages
9
Reaction score
0
A centrifuge is a device in which a small container of material is rotated at a high speed on a circular path. Such a device is used in medical laboratories, for instance, to cause the more dense red blood cells to settle through the less dense blood serum and collect at the bottom of the container. Suppose the centripetal acceleration of the sample is 8.75 x 103 times as large as the acceleration due to gravity. How many revolutions per minute is the sample making, if it is located at a radius of 2.80 cm from the axis of rotation?

1st - figured out the accelration = 8.75E3 * 9.8 = 155 m/s
2nd converted it to m/hour 155 m/s * 60s/h = 9300 m/h
3rd calculated the total distance of 1 rotation = 2*.28*pi = 1.76 m
4th divided velocity / distance = 5284 rpm

But it says my answer is incorrect. What am I doing wrong (beside working on physics homework at 3am)?

Thanks!

-Serena
 
Physics news on Phys.org
8.75 x 10^3?
why change to m/hour?
a=w^2*r, find w and then find the answer.
 
She meant m/min - there are only 60 seconds in a minute, and the problem asks for revolutions per minute.

Serena, I've not worked through the whole thing, but I do see a problem in your step 1. You have 8.75 x 10^3 times about 10, but you end up with 155. It should be on the order of 10000. Also, the units are m/s^2, not m/s, but I assume that was a typo.

Your methodology looks fine, though.
 

Similar threads

Calculating revolutions per minute
  • · Replies 4 ·
Replies
4
Views
3K
Uniform Circular Motion of a centrifuge
  • · Replies 4 ·
Replies
4
Views
2K
What is the angular speed in revolution per minute?
  • · Replies 3 ·
Replies
3
Views
3K
How Do You Calculate Revolutions Per Minute for an Astronaut in a Centrifuge?
  • · Replies 8 ·
Replies
8
Views
10K
How Do You Calculate Centripetal Acceleration in a Blood Centrifuge?
  • · Replies 8 ·
Replies
8
Views
2K
Calculating Revolutions Per Minute of a Ball
  • · Replies 3 ·
Replies
3
Views
6K
Revolutions per sec (centripital acceleration)
  • · Replies 6 ·
Replies
6
Views
2K
MHB Ferris Wheel Rotation: How Many Degrees Per Minute?
  • · Replies 2 ·
Replies
2
Views
2K
Centripetal acceleration centrifuge
  • · Replies 5 ·
Replies
5
Views
3K
How Many Revolutions Per Minute to Equal Free-Fall Acceleration?
  • · Replies 11 ·
Replies
11
Views
3K