# momentum ko conserve kardo

Q: A ball hits the floor and rebounds after an inelastic collision. In this case,

a) the momentum of the ball just after collision is the same as that before collision.
b) the mechanical energy of the ball remains same during the collision.
c) the total momentum of the ball and the earth should be conserved.
d) the total energy of the ball and the earth is conserved.

The answer given in bookI must say this is IITJEE 1986 question)

But i feel the answer must be C only.

Whatsay?

Cheers..!

71
Vivek @ Born this Way ·

It is C and D

71
Vivek @ Born this Way ·

@bond001,

Yes certainly, that energy is lost from the ball, but did u consider whether does it goes? It is added to the atmosphere of the surrounding and hence if the system constitutes of Earth and Ball, the Energy is conserved.

It is just like the entropy of the system decreases but that of surrounding increases. (Don't take this completely similar. Both are different. It's just an example)

1
kunl ·

yosubhosubhi

1

People going for (A) are wrong as magnitude of momentum is same but not the direction! Momentum is a vector quantity so we define its direction also and after collision, speed is same but direction is opposite of the initial one! So technically velocity changes. (C) is definitely correct and even D.

1
Athenes Analyst ·

Ok I have the solutions of IITJEE 1986 question paper and here the answer is..... (C) only.

Momentum conserve ho gaya par energy nahi :P

11
CARLOS ESPIRIDIÃ“N ·

actually the floor is immovable mass...and there external force is acting(Normal force)....hence momentum can not be conserved...

1
sagnik007 bhattacharya ·

must be option "d".....
no confusion bout dat nd "c" is also correct..

1
Athenes Analyst ·

@vivek, I thought in total energy we count only the sum of Potential energy and kinetic energy.

1
Athenes Analyst ·

An old post...... but C is only answer since in inelastic collision some energy may be wasted in form of heat !

11
CARLOS ESPIRIDIÃ“N ·

I think only D is the correct ans..

6
AKHIL ·

i think it shud be C and D.......
ya the total energy of the SYSTEM is conserved

1
Ricky ·

I think the answer is both " ( c ) " and " ( d ) " . Why " ( c ) " is correct is not a matter of controversy . But in inelastic collisions , as far as I know , only the " Kinetic Energy " is not conserved , the total energy remains constant throughout the entire " episode " . Hence , I think " ( d ) " is also one of the answers .

1
shubhi gupta ·

Chahe woh elastic ho ya inelastic ho, just before and after the collision momentum is conserved whereas in inelastic collisiion long before and long after the collision there may not be conversed.....

1
Abhisek ·

@ Subhi : Option(A) pakka kaise ?? Inelastic collision so velocity decrease karega, and so will linear momentum ! [41]

71
Vivek @ Born this Way ·

Subhi.. See the option (C) also and look for the difference....

1
shubhi gupta ·

Bhai (A) toh pakka h....

1
learner ·

i go for only c
how on the earth, energy has started to be conserved in inelastic collisions...
during inelastic collision we have some heat dissipated ....
we may say the energy of the earth +ball conserved ,if taken in account the heat dissipated

1
shubhi gupta ·

the answer must be (A), (C), (D)

1
kunl ·

bakshi
tell me how many scuh assumptions u got to make in physics aur how many have u made till date??

49
Subhomoy Bakshi ·

:-/

then u mean ball+earth=entire universe!

Whatever neways thanks! :)

1
kunl ·

for me "d" is right

unless u start arguing and saying that earth only means land.....and not atmosphere...so we won't count heat given out to atmosphere and hence d is wrong....which is really dumb i feel!

1
kunl ·

simpole and dumb question answer is "c" and "d" as rightly elaborated by ricky