1i think i know the shorter process i saw it in book
it was written that
Mg-N=MLa(alpha)/2
NL/2 = ML2a(alpha)/12
La(alpha)/2 = 3N
then finaaly
N = Mg/4
i didn understood the last two steps
a rod of mass M n lenght L is standing in vertical position,it is pushed with infinitimesly small force ,n fall down in a quarter circle without displacing its lower end then wat is the normal reaction when is at horizontal position?
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14 Answers
62Ask these quesions.. I think that will solve this problem...
Can u balance energy?
What will be the omega when the rod reaches the horizontal state
What will be the fbd of the rod then!
162yes i will explain.. let me draw the fbd and post..
it has nothing to do with anythign else...
62
here the equations will be
mg-R=ma
also balance torque about the point of contact
also mgl/2=Iα
I=mL2/3
hence,
Lα=3/4g
also, αL/2=a
hence, a=3/4g
now put this in first equation
you get mg/4=R
1ya i got it thank u.........
plz can u explain me in wat conditions do we take torque??
62basically having rotation means that there is some angular velocity.
If this angular velocity changes we take torque....
This was not a very straigth forward quetion..
solve some more problems on torque.. you will understnad..
for mechanics (other than kinematics) you could try IRODOV..
there are a lot of quesitons aroudn 10-15 very good ones on rotational..
if you can understand them, then u will probably not solve anything incorrectly!!! (not exxagerrating :) but then in physics three are infinitely many unsolvable (tough) cases.. :)
1hey in ur solution it shld be
La(alpha) = 3/2g not
3/4 g
n one more question ques y has the R is frm point of pure rotaion???
62oh yes.. u are right.. :) tx for pointing out
See the trick is to chose the point where to balcance torque..
Here the component of normal reaction became zero...
generally a point of application of some force is taken so that we dont have to worry aobut the torque due to the forces at that point
that is why you will see a lot of problems with torque balanced at center of mass( gravity acts thre!)