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28. We adopt the positive direction choices used in the textbook so that equations such as
Eq. 422 are directly applicable. The coordinate origin is throwing point (the stone’s
initial position). The
x
component of its initial velocity is given by
vv
x
00
0
=
cos
θ
and the
y
component is given by
y
000
=
sin
, where
v
0
= 20 m/s is the initial speed and
θ
0
=
40.0° is the launch angle.
(a) At
t
= 1.10 s, its
x
coordinate is
xv
t
==
°
=
20 0
110
40 0
16 9
cos
.
.
cos
.
.
m/s
s
m
b
gb
g
(b) Its
y
coordinate at that instant is
()
(
)
2
22
11
sin
20.0m/s 1.10s sin 40.0
9.80m/s
1.10s
8.21m.
yv
t
g
t
=−
=
°
−
=
(c) At
t'
= 1.80 s, its
x
coordinate is
x
=°
=
20 0
180
40 0
27 6
..
c
o
s
.
.
s
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 Spring '08
 Any
 Physics

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