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A packet dropped from a helicopter drops down 5 mts in the 1st second.in the next second it falls 15 mts further,in next,25mts and so on...in the last second it falls 115 mts more and hits the ground. How much time it take to reach the ground? How high the helicopter when the packet was released?

This is an A.P
Here the series is 5,15,25,...115.
a = 5 , d = 15 - 5 = 10 and tn = 115
a + (n - 1)d = 115
5 + (n - 1 ) 10 = 115
ie, 5 + 10n - 10 = 115
10n = 115 + 5 = 120
ie, n = 12
It reach the ground in 12 seconds.


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