Physics
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(t)=(1/2)gt^2+v_0t+s_0
s_0=70m, v_0=11m/s, g=9.8m/s
We want t for s(t)=0
0=(1/2)9.8t^2+11*t+70
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
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