Question

A ball is dropped from a balloon going up at a speed of 7 m/s. If the balloon was at a height 60 m at the time of dropping the ball, how long will the ball take in reaching the ground?

Answer 1

Solution :

Initially ball is going upwards 

Initial velocity=u= -7m/s

S=60m

a=g=10m/s2

From Second equation of motion 

s=ut+1/2at²

60= - 7t +(1/2 )10 t²

60=-7t +5t²

5t² -7t -60=0

t=-7±√49-4x5(-60)/2x5

t=-7±√49+1200/10

t=-7±35.3/10

t=7+35.3/10 =4.2 sec [ as t cannot be negative]

∴ The ball will take 4.2 sec to reach the ground.