Question

A stone is dropped from the hight of 20 m how long will it take to reach the ground???? ​

Answer 1

Height, s=20m

Initial velocity, u=0

Acceleration due to gravity, g=10 m/s  

2

 

Final velocity, v=?

Time taken, t=?

(i) Using relation,

s=u t+  

2

1

​  

gt  

2

 

20=0×t+  

2

1

​  

×10×t  

2

 

20=0+5t  

2

 

t  

2

=  

5

20

​  

=4

t=  

4

​  

=2 s

(ii)For  a freely falling body:

v  

2

=u  

2

+2gh

=(0)  

2

+2×(10)×(20)

So, v  

2

=400

v=  

400

​  

=20 m/s

The speed of stone when it hits the ground will be 20m/s.