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47. Review Conceptual Example 14 before attempting this
problem. Two identical pellet guns are fired
simultaneously from the edge of a cliff. These guns impart an initial speed
of 30.0 m/s to each pellet. Gun A is fired straight upward, with the pellet
going up and then falling back down, eventually hitting the ground beneath
the cliff. Gun B is fired straight downward. In the absence of air
resistance, how long after pellet B hits the ground does pellet A hit the
ground? |
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The total displacement of both
pellets is the height of the cliff which we do not
know. What we do know is pellet A,
fired up will travel to some max height.
It will stop and then begin to fall again. When it reaches the top of the cliff, it
will have the same magnitude of velocity but now will be
pointed down, the same as the second pellet B. So the difference
in time between the two pellets landing is the time Pellet A is traveling
above the cliff height. |
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The change in height for
Pellet A while above the cliff is zero so |
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Either t = 0 which is the
start time or |
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Finding the time from this is |
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