Question

an stone is fall from the top of the tower of height 100m. What will be its velocity just before hitting the ground

Answer 1

Answer:

Height, h = (100 - x)

Initial velocity, u = 0

Time, t =?

g = 10 m/s2 (As the stone is falling down)

We know that,

Putting the values in above equation

(100 – x) = 0 × t +1/2× 10 × t2

(100 - x) = 5t2 (i)

(ii)Now, for stone projected vertically upwards:

Height, h = x

Initial velocity, u = 25 m/s

Time, t =?

g = -10 m/s2 (As the stone is going up)

We know that,

Putting the values in above equationx= 25×t+1/2×(-10)×t2

x = 25t – 5t2 (ii)

Now, by adding (i) and (ii), we get:

100 – x + x = 5t2 + 25 t – 5t2

100 = 25 t

t =

t = 4 s

Therefore, the 2 stones will meet after a time of 4 seconds.

Now, putting the value of t in (i), we get:

100 – x = 5× (4)2

100 – x = 5× 16

100 – x = 80

100 – 80 = x

x = 20m