IIT JEE , AIEEE Forum - Physics , Mechanics

shefy

a bag of sand of mass M is suspended by a string.A bullet of mass m is fired at it with velocity v and gets embedded into it.What is the loss of kinetic energy in this process ?

shashankparewar

this is simple .just conserve the momentum of the system and you will get the velocity of the bullet bag system .remember the velocity of the bag and the bullet are the same after collision.find the diff of the kinetic energies .

Little_Master

When we do as suggested by shashankparewar we get

loss in K.E. = 1/2 mv² (1 - m/(m+M))

But if the bullet pierces more deeper into the sand bag will there not be any difference in loss compared to the bullet remaining on the surface ?

ganesha1991

@ little master
that can be neglected
there wont be much of a difference

when the bullet gets embeded it almost loses all its velocity
so the velocity later can be neglected

harsh.anurag

mv=(M+m)V
V=mv/(M+m)
k.e1=1/2*m*v*v
k.e2=1/2* m *mv/M+m (I HAVE TAKEN MASS AS m BCOZ WE HAV 2 FIND THE LOSS IN KINETIC ENERGY OF BULLET WHOSE MASS IS m AND AFTR STRIKING ITS VELOCITY IS mv/M+m)......

SO MY LOSS IN KINETIC ENERGY IS COMING AS mv/2(v-m/M+m)

RATE IF USEFUL .............
CORRECT IF WRONG.........

shashankparewar

see as soon as the collision occurs the velocity of bag and the bullet becomes same so their relative velocity is zero how can the bullet piersce the bag.

shashankparewar

we have to calculate net energy lost by the system .the velocity mv/m+M is of the bag bullet system so the kinetic energy will be that of the bag bullet system so you have to multiply the velocity of the system with M+m not as harsh.anurag has done.

varun.tinkle

SO MANY ANSWERS AND SO MUCH CONFUSION
SEEE DUDES IT ACCORDING TO WHAT I UNDERSTAND
THE QUES IS ASKING THE LOSS OF KINETIC ENERGY IN THE SYSTEM
SO
ASSUMING THE SAND BAG WAS INITIALL AT REST
BOTH THE MASSES ARE MOVING WITH THE SAME VELO
SO
mV=(M+m)V2
V2=mV/(m+M)
INITIAL .E. OF THE BULLET=1/2mV^2
FINAL K.E.=1/2(M+m)(mV/(m+M))^2
=1/2(mv)^2/M+m
SO LOSS IN K.E.
CAN BE EASILY CALCULATED
PLS RATE ME IF U FIND ME USEFUL
!!!!!!!!!CHEERS!!!!!!

shefy

frnds answer is 1/2mv^2*M/M+m

shefy

dunno how??

shashankparewar

varun.tinkle has done right.

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