Physics Help Forum Free falling object?

 Kinematics and Dynamics Kinematics and Dynamics Physics Help Forum

 Sep 6th 2008, 03:01 PM #1 Junior Member   Join Date: Sep 2008 Posts: 1 Free falling object? A physics teacher performing an outdoor demonstration suddenly falls from rest off a high cliff and simultaneously shouts. When she has fallen for 3.0 s , she hears the echo of her shout from the valley floor below. The speed of sound is 340 m/s. From the information, I got that the cliff is 530 m (2 sig figs) I need to find how fast she will be moving right before she hits the ground, neglecting air resistance of course. I don't know why it's a girl physics teacher... But yeah. If I could just get a starting point that'd be great. Thanks!
Sep 6th 2008, 09:41 PM   #2
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 Originally Posted by colombo A physics teacher performing an outdoor demonstration suddenly falls from rest off a high cliff and simultaneously shouts. When she has fallen for 3.0 s , she hears the echo of her shout from the valley floor below. The speed of sound is 340 m/s. From the information, I got that the cliff is 530 m (2 sig figs) Mr F says: Close enough. I get 532 m. I need to find how fast she will be moving right before she hits the ground, neglecting air resistance of course. I don't know why it's a girl physics teacher... Mr F says: I do. But yeah. If I could just get a starting point that'd be great. Thanks!
u = 0 m/s
a = 9.8 m/s^2
x = 532 m
v = ?

Substitute into $\displaystyle 2ax = v^2 - u^2$ and solve for v.

Actually I'm amazed you can do what I consider the (relatively) difficult problem but can't do what I'd have thought was the (relatively) simple problem!

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