Homework Help: Math

Posted by Jessica on Sunday, November 25, 2012 at 8:25pm.

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, Sunday, November 25, 2012 at 8:57pm
the height h at time t is given by

h(t) = 480 - 16t - 16t^2
when it hits the ground, h=0, so solve
30-t-t^2 = 0
(6+t)(5-t) = 0
t = 5 sec.

the velocity v at time t is

v = -16 - 32t
v(5) = -16 - 160 = -176 ft/s

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