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274
Linear Momentum and Collisions
P9.57
We hope the momentum of the wrench provides enough recoil so that the astronaut can reach the
ship before he loses life support! We might expect the elapsed time to be on the order of several
minutes based on the description of the situation.
No external force acts on the system (astronaut plus wrench), so the total momentum is constant.
Since the final momentum (wrench plus astronaut) must be zero, we have final momentum
=
initial
momentum
=
0.
mv
m
v
wrench wrench
astronaut astronaut
+=
0
Thus
v
m
astronaut
wrench wrench
astronaut
kg
m s
kg
ms
=−
0500
200
80 0
0125
..
.
.
bg
b
g
At this speed, the time to travel to the ship is
t
==
=
30 0
240
4 00
.
.
m
0.125 m s
s
minutes
The astronaut is fortunate that the wrench gave him sufficient momentum to return to the ship in a
reasonable amount of time! In this problem, we were told that the astronaut was not drifting away
from the ship when he threw the wrench. However, this is not quite possible since he did not
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 Fall '11
 Staff
 Physics, Momentum

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