Question

a stone is dropped from a bridge and hits the water after 2 sec.Find the height of the bridge

Answer 1

we know formula s = ut + 1/2at^2
herr u = 0 as it is dropped from rest
s = 1/2 at^2
a = gravity
gravity may be taken as 9.8 or 10 apprx
s = 5t^2 [ g =10]
s = 5(2)^2
==5(4)
ans is 20

if g is 9.8 ans would be 19.6

Answer 2

Hey

we know

acceleration(a) = velocity /time=v/t

and

velocity =distance /time=x/t
put it in acceleration then we get

acceleration =1/t(x/t)= x/t^2


when a free fall then acceleration = gravity (g)=9.8 ~ 10

a=x/t^2

then
x=a* t^2

in question t=2sec

a=9.8

put on above equation

x=9.8*(2)^2= 9.8*4 =39.2 m

if we take
a=10
then
a= 10 *4=40m

so height of bridge =39.2 m or 40m

thanks for asking