IIT JEE , AIEEE Forum - Physics , Mechanics - Conservation of momentum (plzzzzz help........

maverick83

Two identical trains a and b are moving with different velocities such that vel. of a is greater than vel. b. Now a packet is thrown out from train a to train b. and from b to a both packets have same mases. now which train will accelerate .

catch_arnnie

the train with velocity 'a' accelerates.

if i'm correct then i'll give the solution...

elessar_iitkgp

If the packets are thrown at the moment when the trains are side by side, then both train move with the same speeds as before. Neither accelerates.

maverick83

Right answer is train a will be accelerate pls give me the complete solution...... will rate you..

catch_arnnie

solution::

In 2D(or in plane of paper), imagine the train moving in horizontal direction & the pacekts are thrown in vertical direction.

now, since the packets are thrown perpendicular to the train so, they will have no relative velocity with respect to the train when they are thrown.

let mass of each train be M & each packet be m

using conservation of momentum on each train when the packets are in air, to the situation when the packets are exchaged.

for train with velocity 'a'

Ma +mb = (M+m) V where V is final velocity of train 'a'

V = (Ma + mb)/(M+m) ----(1)

for train with velocity 'b'

(Mb + ma) = (M+m) v where v is final velocity of train 'b'

v = (Mb + ma)/(M+m) ------(2)

now, M>>m & a>b

so, observing & comparing v & V from (1) & (2) shows us that train 'a' should accelerate.

i hope this is a convincing answer.

elessar_iitkgp

I was wrong.
Excellent work arnie

arunsrikantperi

maverick83

Thanks errian.....

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