Question

A stone is thrown vertically up from the tower of height 25m with a speed of 20m/s time taken to reach the ground?

Answer 1

let upward direction be positive
s=-25m
u=20 m/s ,g=-10m/s^2
using equation
s=ut +!/2 at^2
-25=20t -5t^2
-5(t^2-4t-5)=0
t^2 -4t -5=0
t^2 -5t+t-5=0
t(t-5)+1(t-5)=0
(t+1)(t-5)=0
t=-1 and t=5
t=-1 not possible
hence t=5

Answer 2

v=0
u=20
t=?
s=25
a=-20/t

so after solving problem we get t time = 2.5seconds