### Free Fall

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Condition where objects are moving through
space neglecting air resistance
Vertically, the only thing acting on the object
is gravity
Acceleration due to gravity:
◦ ag = 9.8 m/s2
A pebble is dropped into a deep well, and the
sound of the splash is heard 3 s later. How
deep is the well? (Ignore the time for the sound to reach
v0 = 0 m/s
ag = 9.8 m/s
t=3s
Given:
◦ v0 = 0 m/s
◦ t = 3s
◦ a = 9.8 m/s2
Equation:
d = do + vot + ½ at2
Trying to find:
◦ d=?
Solve:
d = 0 +(0)(3) + ½ (9.8)(32)
d = 44.1 m
A ball is thrown vertically upward with a speed
of 25 m/s.
– How high does it
– How long does it
– How long does it
– What is its speed
vf = 0 m/s
ag = -9.8 m/s
v0 = 25 m/s
rise?
take to reach its highest point?
take to reach the ground again?
when it returns to the ground?
v0 = 0 m/s
ag = 9.8 m/s
Given:
◦ v0 = 25 m/s
◦ vf = 0 m/s
◦ a = -9.8 m/s2
Trying to find:
◦d=?
◦t=?
Equation:
Solve:
(0)2 = (25)2 + 2(-9.8)(d)
d =31.9 m
Equation:
vf = vo + at
Solve:
0 = 25 + (-9.8)(t)
t = 2.55 s
Given:
◦ v0 = 0 m/s
◦ d = 31.9
◦ a = 9.8 m/s2
Trying to find:
◦ vf = ?
◦t=?
Equation:
Solve:
(vf)2 = (0)2 + 2(9.8)(31.9)
vf = 25 m/s
Equation:
vf = vo + at
Solve:
25 = 0 + (9.8)(t)
t = 2.55 s
Time up = Time Down
•The distance up is the same as the
distance down
•the acceleration is the same, just moving
in an opposite direction
•Therefore is must be the same time!
Velocity up = Velocity Down
•The distance up is the same as the distance
down
•the acceleration is the same, just moving in
an opposite direction
•the time is the same
•Therefore it must be the same velocity!
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Chapter 5
#67, 70, 71, 74, 76
Due Wednesday
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