The center of rotation method:
Apply when
1)ONLY 1 rigid body, with a center of rotation.
2)Take torques about the center of rotation, assuming all bodies to be at rest in equilibrium.
3)The moment of inertia is calculated by assuming all masses to be present as point masses where the thread is wound/ plank is kept.
With each figure, i have attached expression giving the angular accn. of the rigid body..Note that i wrote them all without lifting pen or paper in a matter of seconds..
Give it some practice..try to first actually derive these expressions..only then you'll have a command over it.
Plz. remember that the moment of inertia of a rigid body about a COR is MK^2+Md^2, where d s the distance of the COR from the COM.
bhaiya ye center of rotation kaise pata chalega kahan par hai and hame accln. to sabke assume karne hi honge na
ReplyDeleteits the point at instantaneous rest..eg:
ReplyDelete1) the point of contact b/w the rigid body and ground.
2) the point of contact b/w the body and thread
..assuming no slipping at these points of contact.
anyways..how many have never used center f rotation methods??
bhaiya u mean to say instantaneous axis of rotation vala point maine to com vale method se hi kiya tha
ReplyDeletebhaiya what have u given here
ReplyDeletei am actually not able to understand
please tell how to use them and when????
thank you
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ReplyDeletebhaiya in the 1st ques both the tensions are in anticlockwise dir.... how did u subtract em?
ReplyDeletewe do not take torques about the center of mass of the spool.
ReplyDeletewe're taking torques about the point of contact between the spool and the ground.
now, consider torques about 'P': the point of contact b/w the spool and the ground ('P' is the point of no slip, or the center of rotation):
m1: m1*g*(2R) anticlockwise.
m2: m2*g*(R-r) clockwise.
ohhh yaa thnx bhaiya now i understood what mistake i was doin.. well i know d fact dat i hav to find direction according to d pt of contact .... bt after doin so many ques where i hav to find torque abt center in dis too i subconciously took direc. acc. to center...:p
ReplyDelete