IIT JEE , AIEEE Forum - Physics , Mechanics

sgyaan

but i m nt gettin d ans if i tk final vel of balloon as 0?

also 4 min vel of d stone don't u think dat final vel shld be 0,even dat 2nd method shld b wrong?

hash_include

even i'm not getting that answer..
and yes i agree with u on the minimum velocity part..
but my answer is comin around 60 m/s!!
wait ill check again..

anchitsaini

hash_include

anchit.. check again.. velocity of baloon after 5 sec = 15 m/s not 50..

madman

why should the velocity be zero?
its given it just touches
it means the force exerted by the stone on the balloon should be close to zero
this will not be satisfied if the velocity of the stone is greater than that of the balloon and if the velocity is lower then the stone will have to go past the balloon and then hit it when the balloon comes up which is not the case
and hash include please tell me my errors

anchitsaini

that was pure (i mean every word of this)
that was pure foolishness , no impurity in that whatsoever

madman

what?

anchitsaini

madman
that was for me
!!!

madman

oh! sorry

hash_include

come to think of it..u r right madman.. the only possibility of the ball having velocity 0 when it meets the balloon is when it has already passed the balloon.. sorry 4 d mistake..
but i think ur soln is wrong..

"distance travelled in the next ts = 7.5t + 0.5*3t^2"
from where did u get that 7.5 from??

"ut - 1/2 g t^2 = 75/2 + 15 t + 3/2 t^2
therefore
1/2 g t^2 = 75/2 -3/2 t^2"

how is this true??

madman

i have edited my previous post
the answer still remains the same
sorry for that

hash_include

yea.. nice working!

anchitsaini

well here is my method --

initially velocity of balloon = 3 t = 15

distance travelled by balloon = 3t ² /2 = 75 / 2

now considering the concept of relative velocity --

u _r = u _stone - u _balloon = u _stone- 15

v _r = 0 when the stone reaches the balloon

s _r = 75 / 2

a _r = - (10 + 3) = - 13

v _r ² = u _r ² - 2 a _r s _r

or

u _r ² = 75 * 13

u _r = 31.22 m/s

= u _stone - 15

hence

u _stone = 46.22 m/s

ganesha1991

edit

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