Question

a stone is dropped from the top of a building and at the same time a second stone is thrown vertically upward from the bottom of the building with speed 25m/s.they cross each other after 4second.the height of the building is?

Answer 1

Let the height of the building be ‘h’.

The second stone is thrown vertically upward with speed 25 m/s.

The height reached by this stone in 4 s is,

y = (25)(4) – ½ (9.8)(4²)

=> y = 100 – 78.4

=> y = 21.6 m

So, in 4 s the first stone that is dropped falls through a height = (h – y)

Thus,

h – y = 0 + ½ (9.8)(4²)

=> h – 21.6 = 78.4

=> h = 100 m

The height of the building is 100 m.