How long is an object in the air?

  • Thread starter soicuw
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  • #1
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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: vf2=2a(delta)x
but im not certain.

The Attempt at a Solution


vf2=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
 
Last edited:

Answers and Replies

  • #2
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.
 

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