posted by Josh .
A rock is thrown vertically upward with a speed of 11.0 m/s from the roof of a building that is 70.0 m above the ground. Assume free fall.
In how many seconds after being thrown does the rock strike the ground?
GOT THIS!!!! t=5.07s
What is the speed of the rock just before it strikes the ground?
I HAVE NO IDEA HOW TO DO THIS!!!
Let's check this
s_0=70m, v_0=11m/s, g=9.8m/s
We want t for s(t)=0
Solving for t 0=-4.9t^2+11t+70
t= -11/9.8 +/-sqrt(121 - 4*(-4.9)70)/-9.8
t = 5.07 so the time is correct
v(t)=-gt+v_0 at t=5.07 v=-9.8*5.07+11=-38.7m/s downward