Question

a stone is dropped freely in the river from a bridge it takes 5 seconds to touch the water surface in a river calculate the distance covered by the stone in 2 seconds

Answer 1

Given : 
Initial speed=u= 0 m/s
time=t=5sec
Case 1)
distance travelled = height of bridge=h m
From second equation of motion:
s=ut+1/2at²h
=0xt +1/2 9.8 x 5 x5h
=122.5m
∴The height of the bridge from water level  is 122.5m

 Case ii)
Distance travelled in 4sec
= (1/2x9.8x4x4)
=16x4.9
=78.4 m
Distance travelled in last second :
 =Distance travelled in 5sec - distance travelled in 4 sec=122.5 -78.4=44.1m
∴The distance covered by stone in the last second is 44.1m

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