Chronology | Current Month | Current Thread | Current Date |
[Year List] [Month List (current year)] | [Date Index] [Thread Index] | [Thread Prev] [Thread Next] | [Date Prev] [Date Next] |
On Mar 5, 2021, at 7:52 AM, Carl Mungan via Phys-l <phys-l@mail.phys-l.org> wrote:
Probably John meant to say the *pulley* has a fixed moment of inertia. The string is massless. It changes radius only because it is thick string wound on top of itself.
On Mar 5, 2021, at 10:23 AM, John Mallinckrodt <ajm@cpp.edu> wrote:
The problem specifies (in physics speak) that the axle has a fixed moment of inertia.
https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fyoutu.be%2FQc1JZ7l-_bM&data=04%7C01%7Cajm%40cpp.edu%7Cc85290d679d24319ff0208d8dfeebe0f%7C164ba61e39ec4f5d89ffaa1f00a521b4%7C0%7C1%7C637505563792080834%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&sdata=lPl6KaZICJIYcV8rFkC7eje5bucdnfuCKMFyajzl0mA%3D&reserved=0
John Mallinckrodt
Cal Poly Pomona
On Mar 5, 2021, at 7:05 AM, Michael Barr via Phys-l <phys-l@mail.phys-l.org> wrote:
In Unit 7 of the AP Physics 1 student workbook. Question 7M : Massive Pulley
In the question there is a stationary pulley with a constant mass hanging
off. As the pulley unwinds the radius also decreases.
In part C of the question the answer key explains that rotational
acceleration will decrease as the pulley unwinds due to less Torque. I'm
confused here. Yes there is less torque but if Torque = I x α, and I =
1/2MR^2, then moment of inertiaA decreases even more, so doesn't angular
acceleration go up. A 1/2 drop in radius causes Torque to drop in half but
inertia to drop 4 times. So, doesn't alpha double (assuming we neglect mass
change).
Am I missing something?
Thanks in advance.
Michael Barr
--
*Please consider the environment before printing this e-mail*
__o
_ `\ <, _
...... ( • ) / ( • ) Lower Your Emissions, Raise Your Voice!
_______________________________________________
Forum for Physics Educators
Phys-l@mail.phys-l.org
https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.phys-l.org%2Fmailman%2Flistinfo%2Fphys-l&data=04%7C01%7Cajm%40cpp.edu%7Cc85290d679d24319ff0208d8dfeebe0f%7C164ba61e39ec4f5d89ffaa1f00a521b4%7C0%7C1%7C637505563792080834%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&sdata=zcGjIt73XOFAS7BI2i9yMq0OuDJH0XKO1OJCKXMypqI%3D&reserved=0
CAUTION: This email was not sent from a Cal Poly Pomona service. Exercise caution when clicking links or opening attachments. Please forward suspicious email to suspectemail@cpp.edu<mailto:suspectemail@cpp.edu>.
_______________________________________________
Forum for Physics Educators
Phys-l@mail.phys-l.org
https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.phys-l.org%2Fmailman%2Flistinfo%2Fphys-l&data=04%7C01%7Cajm%40cpp.edu%7Cc85290d679d24319ff0208d8dfeebe0f%7C164ba61e39ec4f5d89ffaa1f00a521b4%7C0%7C1%7C637505563792080834%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&sdata=zcGjIt73XOFAS7BI2i9yMq0OuDJH0XKO1OJCKXMypqI%3D&reserved=0
-----
Carl E. Mungan, Professor of Physics 410-293-6680 (O) -3729 (F)
Naval Academy Stop 9c, 572C Holloway Rd, Annapolis MD 21402-1363
mailto:mungan@usna.edu https://nam11.safelinks.protection.outlook.com/?url=http%3A%2F%2Fusna.edu%2FUsers%2Fphysics%2Fmungan%2F&data=04%7C01%7Cajm%40cpp.edu%7Cc85290d679d24319ff0208d8dfeebe0f%7C164ba61e39ec4f5d89ffaa1f00a521b4%7C0%7C1%7C637505563792080834%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&sdata=SrNxHaoxlDQRCp58Prr4SCfDt%2B25U%2FLtm1EU3EMvc2Y%3D&reserved=0
_______________________________________________
Forum for Physics Educators
Phys-l@mail.phys-l.org
https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.phys-l.org%2Fmailman%2Flistinfo%2Fphys-l&data=04%7C01%7Cajm%40cpp.edu%7Cc85290d679d24319ff0208d8dfeebe0f%7C164ba61e39ec4f5d89ffaa1f00a521b4%7C0%7C1%7C637505563792080834%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&sdata=zcGjIt73XOFAS7BI2i9yMq0OuDJH0XKO1OJCKXMypqI%3D&reserved=0
CAUTION: This email was not sent from a Cal Poly Pomona service. Exercise caution when clicking links or opening attachments. Please forward suspicious email to suspectemail@cpp.edu<mailto:suspectemail@cpp.edu>.