IIT JEE , AIEEE Forum - Physics , Mechanics

shreyaarya

a shell is fired from a canon.it explodes in mid air.its

a) momentum increases

b)momentum decreases

c) K.E increases

d) K.E decreases

e) none of these

abhi3_raj

the answer is e.
this is because the explosion is due to internal force so momentum is conserved.also just before and after the collission there is no change in the potential energy of the system so kinetic energy is also conserved

abhi3_raj

RATE ME IF ITS CORRECT

learner

When it explodes,momentum is conserved,so its neither a nor b.

Further,kinetic energy will also be constant.

So I think its e.

srivathsan

i feel ur question is not complete!!

u say " its momentum ,its ke etc."

what do u mean by its?????

the whole shell?

once it explodes we can only speak abt the fragments!!

please make it cleare!

srivathsan

if it is the case of the fragments ........

then i suppose the internal energy accelerates the pieces and there would be a increase in velocity relatively to the one when the pieces are together as a shell.

so i prefer "increase in kinetic energy"

option "c".

learner

Hey,but the fragments will move in opp directions right?Then when you consider theeir total velocity,I think it will be the same as initial.On the other hand,I think the speed will increase as the direction doesnt matter.

srivathsan

i guess that the internal energy doesnt have any say with the motion of the shell initially.......but when it increases rapidly itmakes the shell to explode...

so i say the fragments will gain some additional velocity r speed as u call it..

jovien09

as far as momentum is concerned , it will be same 'cause the explosion was not because of any external force.....
and foe K.E i think it will be same(considering the velocity of the c.o.m which will be unchanged).

karansingh

again, this question is from NSO, am i right?

answer is C.

as force is internal, momentum is conserves.

KE increases as
KE (final) = KE (initial) + Chemical Energy released during explosion

rate if found useful

sarthak321

i support karan

little_genius

momentum remains conserved.........

kinetic energy remains conserve dsince potr engy =cons.

ganesha1991

since no external force acts
momentum will be conserved
but as for the kinetic energy it will decrease
as some energy will be converted into heat and other energies

x4

GUYS GANESHA IS PERFECTLY RIGHT .

THE QN DOESNT SPECIFY ANY EXTERNAL FORCE SO MOMENTUM IS CONSERVED .

AND SEE A PART OF THE K.E IS CONVERTED TO HEAT , SOUND , LIGHT . ALL FORMS OF ENERGY . SO NET ENERGY DECREASES .

sahilgupta_iit

there is no net external force in the horizontal direction, so momentum is conserved in the horizontal direction,

2mv_i= mv₁ - mv₂ ..... (let 2m be the mass of the shell)

as both the subparts must go in the op

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