Question

A particle of mass1 moving with velocity v collides with mass2 at rest,then they get embedded.Just after collision,velocity of the system:

a)Increases
b)Decreases
c)Remains constant
d)Becomes zero

Answer 1

@hartnn @experimentX @dibuaman @ganeshie8

Answer 2

Its completely in elastic collision so both the masses are joined. And because we are assuming the impulse to be of very short time in x direction and there is no external force that is being applied on this complete system, just use simple momentum conservation
m1v1 + m2v2 = (m1+m2)v3 and find v3

Answer 3

sorry i meant it as "completely in-elastic"

Answer 4

and in completely in-elastic collision there is always energy loss, so i hope i have given you enough hint to get the answer

Answer 5

@dibuaman so what is the answer?

Answer 6

sorry but i cant say, i have been given a warning already, i am new to this website. Btw i have mentioned the answer indirectly in my last comment

Answer 7

@Hero @skullpatrol @primeralph @Psymon

Answer 8

@Mashy

Answer 9

Energy lose means? :)

Answer 10

to loose energy.

Answer 11

@hartnn

Answer 12

the answer is d become zero

Answer 13

how?

Answer 14

d cant be the answer, it can only happen if mass m2 is infinity or if it is held steady.

Answer 15

initially velocity of the system is v(sys) = (m1v1 +m2v2)/(m1 + m2)
so it comes to m1v1/(m1 + m2)

and when we do momentum balance at the moment it strikes
m1v1 + m2v2 = (m1 + m2) v3
so v3 = m1v1/(m1 + m2)
and now the system velocity is v3 which is same as before.
I am assuming head on collision and particles are, well, just particles..

Answer 16

thank you for your great help... @dibuaman

Answer 17

you are welcome!

Answer 18

what nonsense.? :O

velocity is not the same as before :O..

Answer 19

imagine.. a bullet with some velocity.. comes and hits u.. gets embedded in u.. you fly(with the bullet inside u)

now tell me what is the velocity with which u fly?!.. same as that of the bullet? more than that of the bullet or less than that of the bullet?

Answer 20

well, if you look at the question properly, its asking us to find the velocity of the system and not just a body...
so velocity of the complete system is same. Though the velocity of m1 is obviously reduced, which you can see by first eqn and velocity of 2nd body is increased.

Answer 21

and if you notice, then energy is lost by the system, calculate inital total energy, which is just kinetic energy = .5(m1v1^2)
and the final kinetic energy is .5((m1 + m2)v3^2). subsitute the value of v3 and then you will find out that kinetic energy of the system is reduced.

Answer 22

nooo

since m1 is embedded into m2, they both travel together with the same velocity!!!!!!

Answer 23

@Mashy, in your case you are just looking at the velocity of your own shot body!
Initially bullet is with velocity v1 and lets assume it has mass m1, and you are at rest with mass m2 and velocity = 0. When the bullet hits you, you feel the reaction and then you try to stabilize yourself because of friction from ground which is a reaction force, If you assume you are in air, then the bullet and you will be pushed ahead with a decreased velocity which is m1v1/(m1 +m2). And if you calculate the initial velocity of system which is m1v1/(m1 + m2), then you will see that both are same. And it has to be same as there is no external force acting on the system, so system doesn't get accelerated. so velocity of system is constant.

Answer 24

u are confusing VELOCITY AND MOMENTUM!!!

u are talking about momentum :D

Answer 25

yes they both travel with same velocity that is m1v1/(m1 +m2). which is lesser than initial velocity of the bullet.

Answer 26

"m1v1/(m1 +m2)" is momentum! not velocity!

Answer 27

And yes i am talking about velocity and momentum both at the same time. In this question coefficient of restitution s taken as 0. so its a completely inelastic collision.

Answer 28

and so they both have to go together.

Answer 29

hello its velocity my buddy! atleast check the dimension and them say something. :D

Answer 30

yea ye sorry :D..

but

the velocity is NOT conserved

momentum is CONSERVED

so velocity reduces..

question asked is what happens to the VELOCITY!!!!

Answer 31

Yes velocity is not conserved. Obviously!! but momentum is conserved. Ans question says about velocity of system. not of teh body ans system velocity remains same. in this case and that i am showing you by the momentum balance.

Answer 32

Question asked is WHAT HAPPENS TO THE VELOCITY OF "SYSTEM" and not the body!

Answer 33

velocity of the SYSTEM

is the velocity with which m1 and m2 are travelling..

which is LESS than the velocity with which m1 alone was travelling!!!

Answer 34

ok lets take numbers


m1 = 10kg coming with 5m/s.. gets embedded into a mass at rest of 10kg and travel together..
what is the velocity of the system.. what is the answer ?

Answer 35

And it is equal to initial velocity of system. just the way center of mass is calculated, velocity of system is also calculated that way. v(sys) = (m1v1 + m2v2)/(m1 + m2)

Answer 36

u answer my question :P

Answer 37

And so initial velocity of system is same as final velocity of system

Answer 38

which i am trying to say

Answer 39

waitooo..

i think i get whats going on here!

Answer 40

when u consider initial velocity ,u are calculating initial velocity of the system .. considering both m1 and m2 huh?

Answer 41

yes!!! question says, if the velocity of the system changes or not...

Answer 42

i don't think thats what it means.. :-/

i don't think u are supposed to take the whole thing as a system and do it..

i think u are supposed to compare intial velocity of m1 with final velocity of m1 and m2 together..

Answer 43

either ways .chuck it.. :P

Answer 44

Yaa... now its upto the person who has asked the question. :P at least concepts are correct..

Answer 45

yes yes.. poorly worded question..