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Unformatted text preview: f the humvee from the speed of
the projectile? QUICK QUIZ 4.5 ANSWER
(d). A simple method for sorting out relative velocities is to assign subscripts to the
velocities and let the subscripts guide you to the correct solution. The velocity of the tank
relative to the ground is vtg, the velocity of the projectile relative to the tank (the barrel
speed) is vpt, and the velocity of the humvee relative to the ground is vhg. If we wish, for
example, to know the velocity of the projectile relative to the ground we use, v pg = v pt + vtg .
Notice how the subscript t’s appear to cancel one another and leave the subscripts p and g.
We then wish to find the velocity of the projectile relative to the humvee. Again adding the
vectors in such a way that inner subscripts appear to cancel, we use v ph = v pg + v gh = v pt + vtg + v gh = v pt + vtg − vhg . The last step reflects the fact that the velocity of the humvee relative to the ground is
opposite the velocity of the ground relative to the humvee. We can visualize the solu...
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 Winter '14

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