Math
posted by Lusi. on .
A stone is thrown vertically upwards from a platform 60meters above the ground. The initial velocity of the stone is 20m/s.The height of the stone above the ground at t seconds is given by: H(t)=20t5t^2+60m.How long does it take for the stone to hit the ground? At what velocity does the stone hit the ground?

what does it mean when it hits the ground? height H(t) = 0. so, since
H(t) = 5t^2 + 20t + 60
= 5(t^2  4  12)
= 5(t6)(t+2)
when do you think it hits the ground?
Then, since
V(t) = 20  10t
you can figure the velocity