Homework Help: Physics

Posted by Koby on Monday, September 20, 2010 at 12:38pm.

Ball is thrown horizontally off a cliff with an initial speed of 20m/s. a) how long does it take the ball to hit the ground 20m below. b)how long would it take to hit the ground if it was dropped from the cliff? c) how long would it take to hit the ground if it was thrown with an intial velocity of 20m/s at 18 degrees below the horizontal?

Not for sure if im doing this right.
For a) I used: change in x=vi*t; t=20m/20m/s
a) 1sec?
b) change in y=vi(of y) *t-1/2(g)(t^2)
20m=0*t-1/2(9.8)(t^2)
20m=4.9t^2
t^2=4.08
t=2.02 seconds
c) got 1.05 seconds, but that doesnt seem right to me, considering my answer for a)

Any help would be appreciated, especially if you can tell me where I'm going wrong.

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