Cal Poly State University, SLO
D. Niebuhr
Physics Department
Winter 2008
Phys 141
Homework Solutions
Chapter 3, 4
Assigned Problems:
Chapter 3
: 3, 7, 10, 18, 22, 26, 31, 45, 47
Chapter 4
: 4, 5, 8, 16, 25, 28, 32, 34, 41, 46
3.3.
Visualize:
Solve:
(a)
C
=
A

B
if
B
r
is directed in the same direction as
A
r
. Size does not matter, except that
A
B
because
C
as a magnitude cannot be negative.
(b)
C
=
A
+
B
if
B
r
is directed opposite to the direction of
A
r
. Size does not matter.
3.7.
Visualize:
The figure shows the components
v
x
and
v
y
, and the angle
θ
.
Solve:
We have,
sin40 ,
y
v
v
= 
°
or
10 m/s
sin40 ,
v

= 
°
or
15.56 m/s.
v
=
Thus the
x
component is
cos40
(15.56 m/s ) cos40
11.9 m/s.
x
v
v
=
° =
° =
Assess:
Note that we had to insert the minus sign manually with
y
v
since the vector is in the fourth quadrant.
3.10.
Visualize: