Here's the question you clicked on:
mailtoarko
i am posting the picture of my question please help friends
if u know how to solve then pls help otherwise please don't interfere unnecessarily
@morganFREEDDOM if muslim doesn't means terrorist . . .
wats that to do with the question
yes it was but not yours Q and answer of your q is that radius of disk varies inversely square to the M.I. so 1/9M.I of the disk must be subtracted from the actual m.I. of the disk
can u explain me the process
first find the actual M.I. of the disk with mass 9M and radius R then subtract M.I. of mass M and radius R/3
then it should be 9/2 mr^2 - ( 1/2*mr^2/9) but in the solution its given 9/2 mr^2 - ( 1/2*mr^2/9 + 1/2m*(2r/3)^2)
well boy i am confused too. . . sorry cant help any further. . . i'll give you a site you try post your question there it might help
Right answer is 4MR² You should use additivity of moments of inertia. 1st work out mass of small missing disc. 2nd work out its moment of inertia about its own axis, then use parallel axis theorem to find its moment about centre of big disc.
See, MI = (MR^2)/2 (normal disc) Let σ be the Mass per unit area So, σ=M/πr^2 area is pi(r^2) - pi{(r/3)^2} = 8/9(pi)(r^2) So the mass of disk given becomes 8/9(M). So acc. to formula (MI = (MR^2)/2) [8/9(M)×r^2]/2=4/9Mr^2 NOW put M=9M and thus MOI=4Mr^2
I'm afraid something is missing there. You need to apply parallel axes theorem somehow. Why do you write M=9M in the end? You should start with the right mass from the beginning.
actually the original mass is 9M which I inputted at last
can u plz post what is wrng in my solution so that it can be corrected
ans is 4 mr^2 first take the mi of actual disk i.e. 9mr^2divided by 2 then subtract the mi of small disk for that mass of small disk is m since mass distribution is uniform so mi of small disk abt its own axis is M(R/3)^2/2 AND THEN APPLYING PARALLEL AXIS THEOREM MI OF SMALL DISK ABT AXIS OF BIGGER DISK IS M(R/3)^2/2+M(R-R/3)^2=MR^2/2 NOW SUBTRACT BOTH THE MI AND U WILL GET 4MR^2 AS THE ANS.....
find mass of disc (cavity) then subtract [intertia of cavity+(mass of cavity) x(distance from cavity axis to actual rotation axis)squared] that gives u answer