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 : 

विकल्प

• `u/g`

• ug

• `(2u)/g`

• `u/(2g)`

Answer 1

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