Physics 2 – Summer Session 2008
Quiz # 1
Question 1
Let
A
= 4
i
+ 6
j
and
B
= 2
i
+
k
.
C
=
A
x
B
is given by
(a)
8
i
(b)
6
i
– 4
j
– 12
k
(c)
6
i
+ 6
j
+
k
(d)
6
i
+ 4
j
+ 12
k
(e)
none of the above
(4
i
+ 6
j
) x (2
i
+
k
) = 8 (
i
x
i
) + 4 (
i
x
k
) + 12 (
j
x
i
) + 6 (
j
x
k
)
= 8 (0) + 4 (
j
) + 12 (
k
) + 6 (
i
)
Æ
Correct answer is (b)
Question 2
Two unequal masses m and 2m are attached to a thin bar of negligible mass that rotates
about an axis perpendicular to the bar.
When m is a distance 2d from the axis and 2m is a
distance d from the axis, the moment of inertia of this combination is I.
If the masses are
now interchanged, the moment of inertia will be
Before: I = m(2d)
2
+ (2m)d
2
= 6md
2
After: I’ = (2m)(2d)
2
+ md
2
= 9md
2
Æ
Correct answer is (c)
Question 3
A particle moves with constant velocity
v
.
The angular momentum of this particle about
the origin is zero.
(b) and (c)
(e)
never
L
=
r
x
p
, where
p
=m
v
is the momentum and
r
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 Summer '08
 CAMPAGNARI
 Physics, Angular Momentum, Rotation, Correct Answer

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