Question
A body of mass m1 moving with velocity u collides with a second body of mass m2 at rest. Find the fractional energy retained by mass m1 after collision. Suppose collisioned be elastic.
Solution
First body:
Mass = m1
Velocity = u
Second body:
Mass = m2
Velocity, u2 = 0
After collision, the velocity of masses m1 and m2 are given by
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Here, we have
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and 
∴
and
Kinetic energy of mass
before collision,
Kinetic energy of mass
after collision,
Therefore fractional energy retained by mass
is given by,
Mass = m1
Velocity = u
Second body:
Mass = m2
Velocity, u2 = 0
After collision, the velocity of masses m1 and m2 are given by
and
Here, we have
and ∴
and
Kinetic energy of mass
before collision, Kinetic energy of mass
after collision, Therefore fractional energy retained by mass
is given by, 
