even if we consider earth + stone + ball as a system, then too the frictional force provided by the heap of sand cannot be considered as internal force. It is a dissipative force. Also if it is the case of perfectly inelastic collision then what is the common velocity of com of heap and ball. I mean the com just shifts. Afterwards it will come to rest. So the momentum is finally becoming zero.
conservation of energy means only conservetion of KE (in this case) You can alternatively look that option as 'No Work is done'.
Now try to answer
bcuzz it can b easily seen dat KE isnt conservd...
abt momentum.. there is a force acting along that axis of motion ( gravity) so i think momentu 2 cant b conserved....
hav u asked any expert???
huge mass or small mass .. u can consider watever u want to b the system.... there is no mass limiti for systems...
take the sand and stone as a system.... ..so there is no external force acting therefore ...momentum is conserved its as simple ...u see we got a looot confused.....and purav....friction .....force both action and reaction ....act on bodies of the system...so the net of it ..is zero....because it is an internal force...but if u consider any one particle as ur system....then it wud do some work...
if i am rigfht then pls rate me...!! hope its clear...if not then ...pls ask ill try my level best to answer it
If you take ball + sand as system then gravity will be external force. (Eqarth applies it on the ball. So momentum changes. Work done => Chg in Kinetic energy. Explain)
I am waiting for a satisfactory answer.
gravitational force acting on earth at any instant = GMm/R^2
ie, the rate of change of momentum of both bodies is same but in opposite directions
so, momentum is conserved
as there was no reference to the system, we must take the entire thing ( universe) as the system
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