Posted by kevin on Tuesday, September 4, 2012 at 2:30pm.
In the problem, please assume the freefall acceleration g = 9.80 m/s2 unless a more precise value is given in the problem statement. Ignore air resistance.
A stone is thrown vertically downward from the roof of a building. It passes a window 15.0 m below the roof with a speed of 24.3 m/s. It lands on the ground 4.75 s after it was thrown.
(a) What was the initial velocity of the stone?
(b) How tall is the building?

physics  Steve, Tuesday, September 4, 2012 at 3:10pm
If building has height H, and stone has initial velocity V,
h(t) = H  15t  4.9t^2
h(4.75) = 0 = H  15(4.75)  4.9*4.75^2
= H  181.81
so, H = 181.81m
H15 = H15t4.9t^2
t = .794
v(t) = V  9.8t
24.3 = V  9.8*0.794
V = 16.52m/s

physics  kevin, Tuesday, September 4, 2012 at 3:17pm
thanks for the assistance, but apparently none of the answers are correct according to my homework checker.

physics  Elena, Wednesday, September 5, 2012 at 11:53am
h=(v²vₒ²)/2•g,
vₒ= sqrt(v²2•gvh) =
sqrt(24.3²2•9.8•15) = 17.22 m/s.
H=vₒ•t+g•t²/2 =
17.22•4.75+9.8•4.75²/2 =192.35 m
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