Question

An object thrown vertically upward reaches a height of 500m . What was its initial velocity? How long will the object take to come back to the earth ? Assume g= 10m/s square

Answer 1

Given,   u (initial velocity)        = u   v (final velocity)          = 0 (as the body is thrown vertically upward)   h (distance travelled) = 500m   t (time of flight)           = t   g (gravitational accl'n)=10 m/s^2
From the equations of motion,     (a)        h = u^2 / 2g           =>  h * 2g = u^2           =>  500 * 2(10) = u^2           =>  500 * 20 = u^2           => 10000 = u^2
                 u = 100 m/s    
    (b)        t = 2u / g           =>  t = 2(100) / 10
                  t = 20 s
Hope my answer helps you..