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# Physics C - Embarrassing WebAssign Question..

## Question

So for 16 on the WebAssign due tonight, I feel like I'm completely missing something.  I algebra-ized two of the kinematics equations [ x=.5(vf+vo)t and vf=vo+at ] and got x=.5(2vo+at)t, hoping that then I could set the two rocks equal to each other because their x values are the same, and then solve for time somehow.  This failed. Miserably.  I looked a little bit at trying to set x=vot+.5at^2 equal to itself, again because the two x values should be the same, but didn't get anywhere.  It feels like you have to make an equation equal to t, and then figure out a way to set that equal to itself (with one side adding the extra time until the second rock is thrown).

Hope this makes some semblance of sense... any suggestions?

## Recommended Posts

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Here's a few hints...  try setting up a kinematic equation to describe the displacement of each of the rocks as a function of time, realizing that stone 2 starts a bit later than stone 1 (i.e. the time for stone 2 could be t-2s).  Then, you know that the displacement of the stones must be the same, so set displacement 1 equal to displacement 2, and solve for the time t.

Does that help at all?

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Thanks!

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