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Homework: Week 8 – Chapter 9 – SOLUTIONS
1.
(96) A 220g ball falls vertically downward, hitting the floor with a speed of 2.5 m/s and rebounding
upward with a speed of 2.0 m/s.
(a)
Find the magnitude of the change in the ball’s momentum.
(b)
Find the change in the magnitude of the ball’s momentum.
(c)
Which of the two quantities calculated in parts (a) and (b) is more directly related to the net force
acting on the ball during its collision with the floor?
SOLUTIONS
(a)
fi
()
mm
ˆˆ
(0.220 kg) 2.0
2.5
ss
m
ˆ
(0.220 kg) 4.5
s
m
ˆ
0.99 kg
s
0.99 kg m s
m
p
∆=
−
=−
⎡⎤
⎛⎞
−
⎜⎟
⎢⎥
⎝⎠
⎣⎦
=
=⋅
⋅
pp p
vv
yy
y
y
GG G
GG
(b)
(
)
(0.220 kg)
2.0
2.5
0.11 kg m s
ppm
−=
−
=
−
⋅
(c)
2.
(910) A 0.50kg croquet ball is initially at rest on the grass. When the ball is struck by a mallet, the
average force exerted on it is 230 N. If the ball’s speed after being struck is 3.2 m/s, how long was the
mallet in contact with the ball?
SOLUTION
av
m
s
av
(0.50 kg) 3.2
0
7.0 ms
230 N
p
F
t
p
t
F
∆
=
∆
−
∆
=
=
3.
(924) Suppose the car in the figure
below (initially traveling in the x
direction, with mass 950 kg) has an
initial speed of 20 m/s, and that the
direction of the wreckage after the
collision is 40.0
o
above the x axis.
Find the initial speed of the minivan
(initially traveling in the ydirection,
with a mass of 1300 kg) and the
final speed of the wreckage.
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View Full DocumentSOLUTION
22
11
tan
mv
θ
=
()
m
s
2
2
(950 kg) 20.0
tan 40.0
tan
12 m s
1300 kg
v
m
°
==
=
and
( )
m
s
f
12
(950 kg) 20.0
11 m s
(
)cos
(950 kg
1300 kg)cos 40.0
v
mm
=
++
°
4.
(928) A 0.470kg block of wood hangs from the ceiling by a string, and a 0.0700kg wad of putty is
thrown straight upward, striking the bottom of the block with a speed of 5.60 m/s. The wad of putty
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 Fall '09
 WOODAHL
 Physics, Momentum, Work

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