Sponsor Message:
Non Aviation Forum
My Starred Topics | Profile | New Topic | Forum Index | Help | Search 
Need Help: Physics!  
User currently offlineFlyVirgin744 From United States of America, joined Jul 1999, 1313 posts, RR: 1
Posted (11 years 4 months 4 weeks 1 day 1 hour ago) and read 1715 times:

Hey guys, I've been stuck on this problem for awhile. Maybe someone can help me.

Figure 11-43 shows two blocks, each of mass m = 3.2 kg, suspended from the ends of a rigid massless rod of length L1 + L2, with L1 = 0.20 m and L2 = 1.8 m. The rod is held horizontally on the fulcrum and then released. What are the magnitudes of the initial accelerations of (a) the block closer to the fulcrum and (b) the other block?

Now the answer to this situation is

0.956 m/s^2 and 8.60 m/s^2. But next time I do it I will get new numbers.

Can anyone help?


Sometimes I go about in pity for myself and all the while a great wind carries me across the sky.
9 replies: All unread, jump to last
 
User currently offlineAirways1 From United Kingdom, joined Jul 1999, 560 posts, RR: 0
Reply 1, posted (11 years 4 months 4 weeks 1 day ago) and read 1696 times:

I've just done a quick calculation, and I think the answers are

(a) 0.16 m/s^2

(b) 1.44 m/s^2

I will post again if I come up with a different answer.

airways1


User currently offlineJetService From United States of America, joined Feb 2000, 4798 posts, RR: 11
Reply 2, posted (11 years 4 months 4 weeks 1 day ago) and read 1691 times:

Ask David B. He's an expert on massless rods.


"Shaddap you!"
User currently offlineStaffan From , joined Dec 1969, posts, RR:
Reply 3, posted (11 years 4 months 4 weeks 1 day ago) and read 1688 times:

Hi,

First calculate the torque around the fulcrum.

T=L2*F2-L1*F1

Then use Newton's second law for rotation

T=I*a/r (r=L in this case) where I=I1+I2 and I1 and I2 are the moment of inertia for each of the two blocks added together (I=mr^2)

This gives a1=(T*L1)/I and a2=(T*L2)/I

I got the answers you posted above doing it this way. Hope it helps!

Staffan



User currently offlineAirways1 From United Kingdom, joined Jul 1999, 560 posts, RR: 0
Reply 4, posted (11 years 4 months 4 weeks 1 day ago) and read 1685 times:

I seem to have the same problem as you - I get a different answer each time.

Now I have (taking g=10N/kg)

(a) 0.99 m/s^2

(b) 8.89 m/s^2

I thought my previous answer seemed a bit low...

airways1


User currently offlineFlyVirgin744 From United States of America, joined Jul 1999, 1313 posts, RR: 1
Reply 5, posted (11 years 4 months 4 weeks 23 hours ago) and read 1674 times:

That was it Staffan, thanks a lot  Smile


Sometimes I go about in pity for myself and all the while a great wind carries me across the sky.
User currently offlineToner From United States of America, joined Feb 2003, 268 posts, RR: 0
Reply 6, posted (11 years 4 months 4 weeks 23 hours ago) and read 1674 times:

http://panda.unm.edu/courses/finley/P160/HW/HW31Sol.html

User currently offlineFlight152 From United States of America, joined Nov 2000, 3388 posts, RR: 6
Reply 7, posted (11 years 4 months 4 weeks 23 hours ago) and read 1668 times:

JetService..your a math expert. Can you ramble off some of your bullshit errr.. math knowledge?

User currently offlineJetService From United States of America, joined Feb 2000, 4798 posts, RR: 11
Reply 8, posted (11 years 4 months 4 weeks 23 hours ago) and read 1659 times:

Flight152, I was going to see if someone else could help first. I hate to be a know-it-all, but after seeing the responses, I guess I have to.

FlyVirgin's first problem is his polyfractals are all askew. He doesn't realize (as most of the population, except me) that whenever you have two opposing unilinial lengths on a reflective plane, it immediately puts the fulcrum in an opposing mass state. This basically inverts your polyfractals incrementally, thus skewing them. To compensate when calculating the overall static basis, all you have to do is place your variables (L) in the same matrix as the subvortex. Otherwise you end up with a coefficient leak. And everyone know that a coefficient leak, while durinominal, is only a raw element in a saturated array. Hope that helps.



"Shaddap you!"
User currently offlineTbar220 From United States of America, joined Feb 2000, 7013 posts, RR: 26
Reply 9, posted (11 years 4 months 4 weeks 19 hours ago) and read 1641 times:

ROFL JetService!!  Big thumbs up  Big thumbs up


NO URLS in signature
Top Of Page
Forum Index

This topic is archived and can not be replied to any more.

Printer friendly format

Similar topics:More similar topics...
Volunteering At A Hospital; Need Help And Advice posted Sat Aug 22 2009 16:24:33 by MCOflyer
Need Help Getting To Sleep posted Thu Jul 16 2009 00:47:34 by Af773atmsp
I Need Help With A Gay Guy... posted Tue Jul 14 2009 17:56:45 by 7324ever
I Need Help Traveling The Mbta Sbway Possible? posted Wed Jun 10 2009 12:31:20 by StarAlliance38
Need Help With Dialing A Number posted Fri May 29 2009 11:14:46 by Wardialer
Need Help With German Language posted Sun Mar 8 2009 16:09:37 by B727
BMW 3 Series Owners, Need Help Re:run Flat Tires posted Wed Feb 18 2009 23:24:38 by FLY2HMO
Need Help In Choosing A Boston Hotel posted Mon Oct 6 2008 15:46:01 by ScarletHarlot
Need Help With A British Saying posted Fri Sep 12 2008 07:34:36 by Don81603
Need Help: Info About ICN posted Fri Aug 22 2008 16:48:08 by Transpac787