A ball is thrown upward from the top of a tower of height 50m with a velocity of 15m/s. Find the time when it strikes the ground. Take g=10m/s2.
A
2s
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B
3s
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C
4s
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D
5s
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Solution
The correct option is D5s The given problem can be shown as
We have u=+15m/s , a=−10m/s2
and s=−50m
From the equation of motion we have s=ut+12at2 ⇒−50=15t−5t2 ⇒5t2−15t−50=0 ⇒t2−3t−10=0
On solving this, we have t=5s and t=−2s
Taking the positive value of time t=5s.
Hence, the time when it strikes the ground is 5sec