Question

A hot- air balloon having initial velocity v0 rises. Stone dropped from this balloon, when it is 135 m height, hits the ground after 9 s. Find the velocity of the balloon.

Answer 1

Using Newton's Law of motion;

s=ut+0.5at^2

where s is the distance 135m

           t is the time 9s

           a is the acceleration -10ms^-2

           the negative sign is due to the initial direction of motion of stone- while it was in the balloon- being opposite to the direction with which the stone accelerates as it falls.

note that since the stone is falling due to the gravitational attraction of the Earth on it, it accelerates at 10ms^-2.

           u=vo ; to be found

so,

135=vo(9)-5(9)^2

135+5(9)^2=9vo

9vo=540

vo=60ms^-1

I hope I've helped...