# Chapter 11 - Test - Page 1180: 16

$-24$ feet /second in the downward direction

#### Work Step by Step

$s(t)=-16t^2+72t$ Thus, we have $v(t)=s′(t)=-16 \dfrac{dt^2}{dt}+72 \times \dfrac{dt}{dt}$ So, $v(t)=-32t +72$ Set $t=3$ Then $v(3)=-32(3) +72=-24$ feet /second in the downward direction

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