6
Chap.9
HW2
Questions
5.
Figure 9-28 shows graphs of
force magnitude versus time for a
body involved in a collision.
Rank the graphs according to the
magnitude of the impulse on the
body, greatest first.
∫
=
−
=
tf
ti
x
ix
fx
dt
F
p
p
Impulse
This is the area under the
F versus t
curve.
In all three cases it is equal to 12
F
o
t
o
so
they all tie
Problems
35.
A 91 kg man lying on a surface of negligible friction shoves a 68 g stone away from
himself, giving it a speed of 4.0 m/s.
What speed does the man acquire as a result?
There are no external forces in the horizontal direction therefore
f
i
P
P
)
v
=
Since the man is initially stationary
0
=
i
P
v
Let +
x
be the direction the stone is thrown, then writing out
f
P
explicitly (
m
s
is the
stone,
m
m
is the man)
s
m
v
m
m
v
v
m
v
m
s
m
s
m
m
m
s
s
/
10
3
4
91
068
.
0
0
3
−
×
−
=
−
=
−
=
⇒
+
=
The negative sign indicates that the man moves in the -x direction, opposite to the
direction of motion of the stone.

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