A boy on a 20 m high cliff drops a stone. One second later, he throws down another stone. Both the stones hit the ground simultaneously. Find the initial velocity of the second stone. (g =10m/s2 )
- 5 m/s
- 10 m/s
- 15 m/s
- 30 m/s
Explanation
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I dropped ⇒ initial velocity =0
time will be given by h=12gt2
t=√2hg=√2×20 m10 m/s2=2 sec
II both reaches simultaneously be so ti,e taken by IInd stone will be
2 sec−1 sec=1 sec
or t′=1 sec
putting it in h=ut'+12gt2
& h=20 m,g=10m/s2
20=u×1+5×1
u=15 m/s
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