A) \[2\,s\]
B) \[3\,s\]
C) \[4\,s\]
D) \[5\,s\]
Correct Answer: B
Solution :
Velocity acquired by the ball after 2 s of drop is \[v=gt=10\times 2=20m/s\] Height fallen by the ball is \[h=\frac{1}{2}g{{t}^{2}}=\frac{1}{2}\times 10\times 4=20\,\,m\] After gravity disappears, speed is constant. \[\Rightarrow \] \[H-h=(v)\times t'\] \[\Rightarrow \] \[80-20=(20)\times t'\] \[\Rightarrow \] \[60=20\,\,t'\] or \[t'3\,\,s\].You need to login to perform this action.
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