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How deep is the lake? velocity physics

by hachi_roku
Tags: kinematics
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hachi_roku
#1
Jan22-09, 12:22 AM
P: 61
1. The problem statement, all variables and given/known data
a lead ball is dropped into a lake from a diving board 5.0m above the water. after entering the water, it sinks to the bottom with a constant velocity equal to the velocity with which it hit the water. the ball reaches the bottom after 3s after it is released. how deep is the lake?


2. Relevant equations



3. The attempt at a solution
i just need a hint. i think i need to find the velocity first but i don't know how.
i'm trying to treat the problem as two different systems. first system would be from the diving board to the water, and the second system would be from the water to the ground of the lake. i can't find the velocity without the time....i need the time that it takes to hit the water but i don't know how to do that
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LowlyPion
#2
Jan22-09, 01:18 AM
HW Helper
P: 5,341
Looks like you pretty much have it.

What velocity does it strike the water with? You know h and g so ...

http://www.physicsforums.com/showpos...63&postcount=2

How long does it take to fall 5m ? T = ... ?

So (3 - T)*V = ... your answer?


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