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Problems Set 5
Chapter 8
10.) We choose that the zero point of the potential energy is the point at which the block comes to rest,
when the spring is compressed. We are dealing with only conservative forces, so that the mechanical
energy in the beginning is equal to the mechanical energy in the end.
The energies are kinetic, gravitational potential and spring potential:
Then, we solve for d, and find
24.)
a.)
The decrease in gravitational potential energy, will result in an increase in kinetic energy.
Then we just solve for the speed.
Similarly for v
c
, we just replace h
b
with h
c
, v
c
=7.67 m/s.
b.)
The net work done from moving from A to C is
31.) The loss of mechanical energy from the beginning to the end is due to the force of friction. Therefore,
we have
if
EE
=
i
g
i
s
g
f
sf
KUUKUU
++=++
2
1
2
0(
)si
n
000
mg
d
x
kx
q
+
+
+=++
2
2
sin
kx
dx
mg
q
=
fifi
UUKK
=
22
11
2
1
2
0
abba
abb
mg
h
mg
h
m
v
mv
mg
h
mg
h
mv
2
2
()
2
2(9.8)(
5
3.20)
5.9
4/
b
ab
b
b
b
v
g
h
gh
v
g
hh
v
v
ms
=
5.00(9.8)(5.0
0
2.00)
147
ac
W
W
WJ
=
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View Full DocumentWe know that the force of friction is just proportional to the normal force on block 1, so we have
We just solve for the velocity.
33.)
a.)
The block starts with kinetic energy and comes to rest. We have
b.)
We set the zero of the potential energy to be at the place where the block starts its motion.
Then after traveling a distance, x, along the plane, the change in the potential energy is
c.)
The change in mechanical energy is from the energy lost to friction. The change in
mechanical energy is
We solve for the force.
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 Fall '06
 Winnokur
 Physics, Energy, Force, Potential Energy

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