#### Answer

Time taken by the object will be 6.73 seconds.

#### Work Step by Step

Distance s(t) in feet travelled by a freely falling object is given by the function $s(t)=16t^2$
The height i.e. s(t) of Hoover Dam is 725 feet.
Time taken will be- $s(t)=16t^2$
Step-1: Substitute s(t) in the formula
$725=16t^2$
Step-2: Divide both sides by 16
$\frac{725}{16}=t^2$
Step-3: Use the square root property
$±\sqrt \frac{725}{16}=t$
$± \frac{26.9258}{4}=t$
$± 6.7314=t$
Since time cannot be negative, $t=6.7314$ seconds which is approximately equal to 6.73 seconds.