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Question
A body is projected vertically upward with an initial velocity u . If acceleartion due to gravity is g , the time for which it remains in air , is :
Options
`u/g`
ug
`(2u)/g`
`u/(2g)`
Solution
A body is projected vertically upward with an initial velocity u . If acceleartion due to gravity is g , the time for which it remains in air , is : `(2u)/g`
METHOD : Let't' be the time in which the body reaches its maximum height.
Initial velocity = u.
Final velocity (at the highest point) = 0.
Acceleration due to gravity = -g (negative sign indicates the body is moving against gravity).
Using the first equation of motion,
v = u + gt.
We get,
0 = u - gt
Or t = u/g
Now total time for which the ball remains in air = Time of ascent + Time of descent
Because time of ascent = Time of descent,
Total time taken = u/g + u/g = 2u/g
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