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प्रश्न
A metal ball of mass 5 kg falls from a height of 490 m. How much time it will take to reach the ground? (g = 9.8 m/s2)
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उत्तर
Given, Mass (M) = 5 kg.
Distance travelled by the ball (s) = 490 m
Initial velocity of the ball (u) = 0
Gravitational acceleration (g) = 9.8 m/s2
Newton's second equation of motion gives
s = `"ut" + 1/2 "gt"^2`
∴ 490 = `0 xx "t" + 1/2 xx 9.8 xx "t"^2` .....[Initial velocity (u) = 0]
⇒ 490 = 4.9 t2
t2 = `490/4.9`
t2 = 100
t = 10 sec.
∴ The ball takes 10 seconds to reach the ground.
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