Question

An object is thrown downward with an initial velocity of 3 feet per second. The relationship between the distance s it travels and time t is given by s = 3t + 16t2. How long does it take the object to fall 70 feet?

Answer 1

Answer:2 s

Explanation:

Given

initial velocity $u=3 ft/s$

distance travel $s=3t+16t^2$

time taken to travel 70 feet

$70=3t+16t^2$

$16t^2+3t-70=0$

using $x=\frac{-b\pm \sqrt{b^2-4ac}}{2a}$ to get roots

$t=\frac{-3\pm \sqrt{3^2-4(16)(-70)}}{2\cdot 2}$

t=2 and -2.19

only feasible time is 2 s

thus it requires 2 s to cover 70 feet