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
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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 !!
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