A stone is thrown straight up from the edge of a roof, 625 feet above the ground, at a speed of 10 feet per second.

Question

1. At what time does the stone hit the ground?
2. What is the velocity of the stone when it hits the ground?

Answer 1

h=625+10t-16t^2=0 feet at ground level

16t^2-10t-625=0

use the quadratic formula, with a=16, b=-10, c=-625

t=5/16+(1/32)sqr(100+64(625))=

about 4.4651 seconds to hit the ground (ignore -3.215)

v=h'=10-32t

v(4.4651)=about 10-32(4.4651)=

-132.882 ft/sec = velocity when it hits the ground