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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