Question

a rock is thrown upward with a velocity of 18 meters per second from the top of a 38 meter high cliff, and it misses the cliff on the way back down. When will the rick be 12 meters from ground level

Answer 1

h=-9.8t^2+18t+36

want h=4

therefore

-9.8t^2+18t+32=0

t=(-1/19.6)-18+/-sqrt(324+1254.4); sqrt term is equal to 39.73, use negative root only

t=(-1/19.6)(-57.73)=2.95 seconds