Question

Can someone explain this........

Q.A girl throws a ball vertically upward with a velocity of 20 m/s.Ignore the air resistance, how long will it take to fall back to her hands, where g the value of 'g' is 10 m/s⁻²?

a) 4 sec
b) 6 sec
c) 2 sec
d) 3 sec
(Ans. 4 sec)

Answer 1

v=u+at

finally ball in air will somewhere stop so v=0

u in upward direction is positive

0=20+(-10)*t

t=2 sec for upward journed

then t=2 sec for downward journey

total time = 4 sec in which ball will come to hand