Posted by Lusi. on Tuesday, December 20, 2011 at 5:50pm.
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?

Math  Steve, Wednesday, December 21, 2011 at 12:02am
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