A ball is dropped from the top of a tower 120m high and simultaneously another ball is projected vertically upwards from the ground with a speed of 30m/s. The two balls will meet after
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 C4s Let ′x′ be the distance from the top of tower, where the balls projected will meet ∴ For ball freely falling body we know that the displacement covered is s=12at2, where t is the time when both balls meet.
⇒x=12gt2...(i)
For ball projected upwards: the displcement is (120−x) 120−x=30t−12gt2 ∴ From (i) and (ii)