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A balloon rises from ground when a stone is dropped from balloon at a given instant it takes a time 2u/g, ( u is constant) to reach ground irrespective of position from where it is dropped. Find acceleration of balloon as a function of time

Asked by hariom2083 16th July 2018, 12:46 PM
Answered by Expert
Answer:
Let h be the height when the stone is dropped from ballon. Let v be the ballon velocity when the stone is dropped.
 
Then for the stone, we can write, S(t) = h + v×t - (1/2)×g×t2 ..................(1)
where S(t) is vertical distance travelled by the stone as a function of time.
 
It is given that at t = (2u)/g , stone reaches ground, i.e., S(t) = 0 when t = (2u)/g.
 
hence from eqn.(1) we write, begin mathsize 12px style h space plus space v cross times space fraction numerator 2 u over denominator g end fraction minus open parentheses 1 half close parentheses cross times g cross times open parentheses fraction numerator 2 u over denominator g end fraction close parentheses squared space equals space h space plus space fraction numerator 2 cross times u cross times v over denominator g end fraction minus fraction numerator 2 cross times u squared over denominator g end fraction space equals space 0 space............. left parenthesis 2 right parenthesis end style
we write the eqn. for balloon speed as, begin mathsize 12px style v open parentheses tau close parentheses space equals space fraction numerator d over denominator d tau end fraction open square brackets h open parentheses tau close parentheses close square brackets space equals space u space minus space open parentheses fraction numerator g over denominator 2 u end fraction close parentheses h space................... left parenthesis 3 right parenthesis end style
In above eqn.(3), the expression for v(τ) is written using eqn.(2)
 
Differential eqn. (3) is solved as follows.
 
begin mathsize 12px style integral d tau space equals space integral fraction numerator d h over denominator u space minus space open parentheses begin display style fraction numerator g over denominator 2 u end fraction end style close parentheses h end fraction
tau space equals space open parentheses fraction numerator 2 u over denominator g end fraction close parentheses space ln open square brackets fraction numerator 1 over denominator 1 minus open parentheses begin display style fraction numerator g over denominator 2 u squared end fraction end style close parentheses h open parentheses tau close parentheses end fraction close square brackets space plus space c o n s tan t

i f space w e space a p p l y space t h e space i n i t i a l space c o n d i t i o n comma space a t space tau equals 0 comma space h open parentheses tau close parentheses equals 0 space comma space w e space g e t space c o n s tan t space equals space 0 semicolon

h e c e space w e space h a v e space tau space equals space open parentheses fraction numerator 2 u over denominator g end fraction close parentheses space ln open square brackets fraction numerator 1 over denominator 1 minus open parentheses begin display style fraction numerator g over denominator 2 u squared end fraction end style close parentheses h open parentheses tau close parentheses end fraction close square brackets space space space space


end style
begin mathsize 12px style space open parentheses fraction numerator g over denominator 2 u end fraction close parentheses tau space equals space ln open square brackets fraction numerator 1 over denominator 1 minus open parentheses begin display style fraction numerator g over denominator 2 u squared end fraction end style close parentheses h open parentheses tau close parentheses end fraction close square brackets space........... left parenthesis 4 right parenthesis end style
 
now we write expression for h(τ) using eqn.(4),  begin mathsize 12px style h left parenthesis tau right parenthesis space equals space fraction numerator 2 space u squared over denominator g end fraction open square brackets 1 space minus space e x p open parentheses fraction numerator g over denominator 2 u end fraction tau close parentheses close square brackets space................... left parenthesis 5 right parenthesis
end style
from eqn.(5) and eqn.(3), we can write
 
 begin mathsize 12px style v open parentheses tau close parentheses space equals space u space minus space open parentheses fraction numerator g over denominator 2 u end fraction close parentheses h space equals space u space e x p open square brackets negative open parentheses fraction numerator g over denominator 2 u end fraction close parentheses tau close square brackets
a c c e l e r a t i o n space a open parentheses tau close parentheses space equals space fraction numerator d over denominator d t end fraction open parentheses v open parentheses tau close parentheses close parentheses space equals space g over 2 space e x p open square brackets negative open parentheses fraction numerator g over denominator 2 u end fraction close parentheses tau close square brackets end style

Answered by Expert 18th July 2018, 3:42 PM
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