Question

a stone is dropped from the top of a tower. if it hits the ground after 10 seconds, what is the height of the tower. ( hint: s=ut -1/2gt^2)

Answer 1

t= 10s 
g = 9.8 m/s²
u = 0
We have
s = ut + 1/2gt²  ( as u = 0, therefore s = 1/2gt²)
s = 1/2 X 9.8 X 10 X 10
s = 490 m.
The height of tower is 490 m.

Answer 2

We know that according to sign convention g should always be -ve.

So using s=ut+at^2/2

So s=0+-10(10)*1/2

   s=-50m

Here -ve sign is due to sign convention.

I hope I am correct.If my way of writing is hard just represent these in your not by writing!!