A stone is dropped from a certain height which can reach the ground in 5 second. If the stone is stooped after 3 second of its fall and then allowed to fall again, then the time taken by the stone to reach the ground for the remaining distance is -
(A) 3 sec (B) 4 sec (C) 5 sec (D) None of these...........
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Let ‘h’ be the height from which the stone is dropped.
Using, S = ut + ½ at^2
=> S = 0 + ½ (9.8)(5^2) = 122.5 m
It is first allowed to fall for 3 s.
Distance it traveled in this 3 s is,
S = ut + ½ at^2
=> S = 0 + ½ (9.8)(3^2) = 44.1 m
When it is released again it will have to fall through a height = 122.5 – 44.1 = 78.4 m
Using, S = ut + ½ at^2
=> 78.4 = 0 + ½ (9.8)t^2
=> t = 4 s
So, the stone will take 4 s to reach the ground after releasing from the stop.
Option B) is correct.
Using, S = ut + ½ at^2
=> S = 0 + ½ (9.8)(5^2) = 122.5 m
It is first allowed to fall for 3 s.
Distance it traveled in this 3 s is,
S = ut + ½ at^2
=> S = 0 + ½ (9.8)(3^2) = 44.1 m
When it is released again it will have to fall through a height = 122.5 – 44.1 = 78.4 m
Using, S = ut + ½ at^2
=> 78.4 = 0 + ½ (9.8)t^2
=> t = 4 s
So, the stone will take 4 s to reach the ground after releasing from the stop.
Option B) is correct.
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