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To estimate the height of a bridge over a river, a stone is dropped freely on the river from the bridge. The stone takes 2 s to touch the water surface in the river. Calculate the height of the bridge from the water level. Take `g=9.8m//s^(2)` |
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Answer» The stone is being dropped freely from rest ,so the initeal velocity of the stone u=0.Again the velocity of stone is increasing as it comes down ,so the acceleration due to gravity g is to be taken as positive . Now Initial velocity of stone u=p0n Time taken t=2 s Acceleration due to gravity `g=9.8m//s^(2)` (stone come down ) Height of the brigdge h=? (to be calculated ) We know that for a freely falline body Height ` h=ut+1/2gt^(2)` Putting the above values in this formula we get `h=0xx2+1/2xx9.8xx4` ` h=1/2xx9.8xx4` h=19.6 Thus the height of bridge above the water level is 19.6 |
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