To an observer, two bodies of equal rest mass collide head on with equal but opposite velocities 2c/5 and cohere. To a s

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To an observer, two bodies of equal rest mass collide head on
with equal but opposite velocities 2c/5 and
cohere. To a second observer, one body is initially at rest. Find
the apparent velocity of the other, moving mass before the
collision and compare its initial energy in the two frames of
reference
calculate v', E, and
E'.