Question

Lacie kicks a football from ground level at a velocity of 13.9 m/s and at an angle of 25.0° to the ground. How long will the ball be in the air before it lands?
Round your answer to the nearest tenth.

Answer 1

Just consider the vertical component
$d_y=v_{0,y}t+\frac{1}{2}at^2$
$d_y=(13.9\sin 25\°)t+\frac{1}{2}(-9.8~m/s^2)t^2 \\ \\ d_y=5.87t-4.9t^2$

Set d_y equal to 0 to find the times the ball is on the ground
$0=5.87t-4.9t^2 \\ \\ 0=t(5.87-4.9t) \\ \\ t=0 \\ \\ t=1.2~s$

The ball was in the air for 1.2 seconds