Question

A boy is standing 490m above the ground on a building. A jet is flying on the mountain . Some people are sitting on a rock on that mountain. An elephant and his owner are walking on the mountain. The elephant drinks some water and have fun.The jet drops 3 missiles. the boy throws a white ball from the building vertically down with initial velocity=0 .What time does the ball take to strike the ground?

Answer 1

for motion of ball
u = 0
s = 490m
a = g = 9.8 m/s²
from s = ut + 1/2 at²
490 = 0 + 1/2 × 9.8 × t²
=490= 4.9 × t²
= 490 ÷ 4.9 = t²
t² = 100
t = 10 sec

Answer 2

Here is your solution

Given

Height = 490m

initial velocity = 0

We have to find time does the ball take to strike the ground?

Using 2nd law of equation. we get:-

s = ut+1/2gt^2
s=0×t+1/2gt^2
s=1/2gt^2
490=1/2×10×t^2
490/5=t^2

$time = 98 \sqrt{2} second$

$time = 7 \sqrt{2}s \\or 9.89s \\time=(10 second\: approx)$

hope it helps you