Respostas

2014-08-12T09:41:50-03:00
T=d/v => t=80/10 = 8s
2014-08-12T13:11:35-03:00
h= \frac{g*t^2}{2}

80= \frac{10*t^2}{2}

80*2=10*t^2

160=10*t^2

t^2= \frac{160}{10}= \sqrt{16}=4s
realmente, também podemos usar t²=d/5 (t²=80/5=>t=√16=> t=4s)