How long is an object in the air?

[soicuw]

Homework Statement

I'm having trouble with questions such as: A kangaroo jumps to a vertical height of 2.7m. How long was it in the air before returning to earth?

Homework Equations

My guess is: v_f²=2a(delta)x
but I am not certain.

The Attempt at a Solution

v_f²=2*-9.8*2.7
it gave the wrong answer. The answer key says t=1.5sec. I need to know how to find this! Thanks

 

[weesiang_loke]

Hi,
You find the incorrect velocity based on your attempt.
the equation used is v^2 = u^2 + 2*a*s, where v = final velocity, u = initial velocity, a = acceleration and s = displacement.
so at maximum height, v = 0 , s = 2.7 and a = -9.8 .
then you will be able to find your initial velocity of the kangaroo, u.

after that just find the time, which i think should be easy.