# physics

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A students on a balcony uses a slingshot to shoots rock straight up

at 29.4 m/s. If the rock takes 8.0 s seconds to hit the ground below the balcony, how high is the balcony above the ground?

• physics -

The velocity 0f the rock is zero at its' max. height:

Vf = Vo + gt = 0,
29.4 - 9.8t = 0,
-9.8t = -29.4,
t = -29.4 / -9.8 = 3s to reach max height
Time in flight = 8s.
Fall time = 8 - 3 = 5s,

d = 0*5 + 0.5*9.8*5^2,
d = 0 + 122.5 = 122.5m to gnd.

h = 122.5 - 44.1 = 78.4m.

= 4.9*3^2,
d = 88.2 - 44.1 = 44.1m up.

• physics -

Oops!!

d (up) = Vo*t + 0.5*gt^2,
d (up) = 29.4*3 + 0.5*(-9.8)3^2,
d (up) = 88.2 - 44.1 = 44.1m.

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