Go Back   Physics Help Forum > College/University Physics Help > Advanced Mechanics

Advanced Mechanics Advanced Mechanics Physics Help Forum

Like Tree1Likes
  • 1 Post By skeeter
Reply
 
LinkBack Thread Tools Display Modes
Old Nov 21st 2017, 03:56 AM   #1
Junior Member
 
Join Date: Nov 2017
Posts: 4
Rotation/Energy

An electric grindstone weighing 2kg and has a diameter of 20cm rotates counterclockwise
at 30 rpm.When power is turned off, it takes 60 seconds before the grindstone stops.

What will be grindstone its angular acceleration before it stops (assume constant
angular acceleration). positive direction - against the clock
.
How many turns will the grind take before it stops?

What is the momentum of tightness to the grindstone (massive cylinder)?

How much kinetic energy is stored in the grindstone in the moment it
turns off?

If we calculate this energy into gravitational energy, how high above the groundmust the grindstone shall be placed?
zawhein is offline   Reply With Quote
Old Nov 21st 2017, 09:18 AM   #2
Senior Member
 
skeeter's Avatar
 
Join Date: Aug 2008
Posts: 110
Originally Posted by zawhein View Post
An electric grindstone weighing 2kg and has a diameter of 20cm rotates counterclockwise
at 30 rpm.When power is turned off, it takes 60 seconds before the grindstone stops.

What will be grindstone its angular acceleration before it stops (assume constant
angular acceleration). positive direction - against the clock
$\alpha = \dfrac{\Delta \omega}{\Delta t} = \dfrac{0 - 30 \, rpm}{1 \, min} = -30 \, rev/min^2 = -\dfrac{\pi}{60} \, rad/sec^2$

How many turns will the grind take before it stops?
$\Delta \theta = \bar{\omega} \cdot \Delta t = \dfrac{(30 \, rpm + 0)}{2} \cdot (1 \, min) = 15 \, rev$

What is the momentum of tightness to the grindstone (massive cylinder)?
I've never heard the term "momentum of tightness" ... contextual clues make me think you mean "moment of inertia". If so,

$I = \dfrac{1}{2}MR^2$

How much kinetic energy is stored in the grindstone in the moment it
turns off?
$K_{rot} = \dfrac{1}{2}I \omega^2$

If we calculate this energy into gravitational energy, how high above the groundmust the grindstone shall be placed?
I'm guessing this means $K_{rot} = U_{grav} \implies \dfrac{1}{2}I \omega^2 = Mgh \implies h = \dfrac{I \omega^2}{Mg}$
benit13 likes this.
skeeter is offline   Reply With Quote
Old Nov 22nd 2017, 02:14 PM   #3
Junior Member
 
Join Date: Nov 2017
Posts: 4
Thanks
zawhein is offline   Reply With Quote
Reply

  Physics Help Forum > College/University Physics Help > Advanced Mechanics

Tags
rotation or energy



Thread Tools
Display Modes


Similar Physics Forum Discussions
Thread Thread Starter Forum Replies Last Post
Kinetic energy of rotation mustaphashehu1 Kinematics and Dynamics 4 Nov 16th 2015 09:33 AM
rotation indira Kinematics and Dynamics 4 Jun 11th 2015 12:25 AM
rotation indira Kinematics and Dynamics 6 Jun 9th 2015 12:13 PM
rotation indira Kinematics and Dynamics 2 Jun 9th 2015 11:17 AM
Rotation Dynamics Doman22 Advanced Mechanics 1 Nov 7th 2008 08:29 PM


Facebook Twitter Google+ RSS Feed