Question

a boy drops a stone from the edge of the roof. It passes a window 2 metre high in 0.1 s . How far is roof from window

Answer 1

Answer:

Window's Length = 2 m

Time taken for crossing = 0.1 seconds

Acceleration of the stone = 10 m/s²

Applying Second equation of Motion, we can find out the speed of the Stone.

⇒ s = ut + 1/2 at²

⇒ 2 = u ( 0.1 ) + 1/2 ( 10 ) ( 0.1 )²

⇒ 2 = 0.1 u + 5 × 0.1 × 0.1

⇒ 2 = 0.1u + 0.05

⇒ 2 - 0.05 = 0.1u

⇒ 1.95 = 0.1 u

⇒ u = 1.95 / 0.1 = 19.5 m/s

Hence the speed of the stone while crossing the window is 19.5 m/s.

Now we must calculate the distance of window from roof top.

Using Third equation of motion we get,

⇒ v² - u² = 2as

The stone started from rest due to which u = 0

⇒ 19.5² - 0² = 2 ( 10 ) s

⇒ 380.25 = 20 s

⇒ s = 380.25 / 20

⇒ s = 19.0125 m

Hence the distance between the roof and the window is 19.0125 m.

Hope it helped !!