#### Answer

$L=1305.61$ lb

#### Work Step by Step

Since $L$ varies jointly as the square of the speed $s$ and the area $A$, we have:
$L=ks^{2}A$
We are given: $L=1700$ and $s=50$ and $A=500$, so we have:
$1700=k*50^{2}*500$
$ k=0.00136$
Therefore:
$L=0.00136s^{2}A$
We plug in $A=600$ and $s=40$ to find $L$:
$L=0.00136*40^{2}*600=1305.61$ lb