# Physics

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Two children are playing on a 154-m-tall bridge. One child drops a rock (initial velocity zero) at
t = 0.
The other waits 1.1 s and then throws a rock downward with an initial speed
v0.
If the two rocks hit the ground at the same time, what is v0

• Physics -

The time of the first rock fall is
t1=sqrt(2h/g)=sqrt(2•154/9.8) =5.6 s.
The time of the second rock motion øs
t2=t1-1.1 =5.6-1.1=4.5 s.
h=vₒt+gt²/2.
vₒ=(h- gt²/2)/t= h/t-gt/2=154/4.5 -9.8•4.5/2 =34.22-22.05=12.17 m/s

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