Answer:
About 1.75 seconds
Explanation:
We use the kinematic equation for free fall under the action of gravity:
[tex]h(t)=h_i -\frac{1}{2} g\,t^2\\0 = 15-\frac{1}{2} 9.8\,t^2\\t^2=\frac{15*2}{9.8} \\t=\sqrt{\frac{15*2}{9.8}} \\t\approx 1.75\,\,sec[/tex]
