Posted by Jessica on .
A rock is thrown straigh down from a height of 480 feet with an initial velocity of 16 feet per second. How long does it take to hit the ground and with what speed does it hit the ground?

Math 
Steve,
the height h at time t is given by
h(t) = 480  16t  16t^2
when it hits the ground, h=0, so solve
30tt^2 = 0
(6+t)(5t) = 0
t = 5 sec.
the velocity v at time t is
v = 16  32t
v(5) = 16  160 = 176 ft/s