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69. (a) We use conservation of mechanical energy to find the speed of either ball after it
has fallen a distance
h
. The initial kinetic energy is zero, the initial gravitational potential
energy is
M gh
, the final kinetic energy is
1
2
2
Mv
, and the final potential energy is zero.
Thus
Mgh
Mv
=
1
2
2
and
vg
h
=
2.
The collision of the ball of
M
with the floor is an
elastic collision of a light object with a stationary massive object. The velocity of the
light object reverses direction without change in magnitude. After the collision, the ball is
traveling upward with a speed of
2
gh
. The ball of mass
m
is traveling downward with
the same speed. We use Eq. 975 to find an expression for the velocity of the ball of mass
M
after the collision:
22
3
2
.
Mf
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This note was uploaded on 05/17/2011 for the course PHY 2049 taught by Professor Any during the Spring '08 term at University of Florida.
 Spring '08
 Any
 Physics, Energy, Kinetic Energy

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