Question

pleasetell this question​

Answer 1

sorry I can't answer you Bhaiya I am in 4 class

Answer 2

According to the equation,  

16t²  + 4t = d

16t²  + 4t = 420

4t² + t − 105 = 0

4t²  −20t +21t − 105 = 0

4t(t−5) + 21(t−5 )= 0

(4t+21) (t−5)=0

t=−$\frac{21}{4}$ or 5

As, time cannot be negative.

Therefore, the required time taken by the stone to fall 420 meter is 5 seconds.

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Thank you.