The velocity of a ball v is thrown vertically upwards is represented by the equation v=5t2+20t−60 where v represents velocity and t represent time in seconds. Calculate the time when the ball stops for the first time.
A
2
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B
3
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C
6
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D
12
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Solution
The correct option is A2 A state of rest is defined as v=0. Hence 5t2+20t−60=0 or t2+4t−12=0 or (t+6)(t−2)=0 or t=−6,2. But t=−6 is not possible. Hence t=2sec.