Kinematics Motion - Tenafly Public Schools

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Free Fall
AP Physics C
Mrs. Coyle
Free Fall

An object moving under the influence of
gravity only.

g = -9.80 m/s2 , downwards

No air resistance.
Free fall is uniform accelerated motion. (g is
constant throughout the motion.)


Galileo: all objects fall with the same
acceleration. He used his ball and channel
experiment.
Remember? Galileo’s Ball and
Channel Experiment
He raised the
channel to a level
that simulates
gravity?
http://www.ifa.hawaii.edu/~barnes/ast110_06/rots/pftim19_01.png
Examples:
 Dropped
 Thrown downward
 Thrown upward
Dropped
Dropped from xo = 0
Position
(m)
o
Time (s)
Parabola
Thrown
upwards
from xo = 0
What is the
velocity and
acceleration
at the top of
the motion?
Example 1

A ball thrown vertically upward is caught by
the thrower after 20.0 s. Find (a) the initial
velocity of the ball and (b) the maximum
height it reaches.

Answer: a) 98.0 m/s, b) 490 m
Example 2

Another scheme to catch the roadrunner has
failed. A safe falls from rest from the top of a
25.0m high cliff toward Coyote, who is
standing at the base. Coyote first notices the
safe after it has fallen 15.0 m. How long does
he have to get out of the way?

Answer: 0.51 s
Example 3

A helicopter is rising and its position is given
by h= 4t2 . After 3 sec it releases a package.
How long did it take for the package to fall to
the ground?

Answer: 6.1 sec

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