Question 30286
The formula to use is: *[tex h=vt-16t^2]
Where:
h=height
v=velocity
t=time in seconds
Plug in the knowns:

*[tex h=65t-16t^2]

Differenate and multiply the results by 2.

*[tex \frac{d(65t-16t^2)}{dx}=65-32t]

*[tex 32t=65]

*[tex t=2.03125]

Multiply the results by 2:

2(2.03125)=4.0625


Or you can factor it:
<pre><b>65t-16t^2
16t(4.0625-t)
t=0 or t=4.0625. ---> this  would be a proving statement, if you were asked to prove it.


<font color = red>Hence, the time it would take is 4.06 seconds.</font>
Paul.