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46. We neglect air resistance, which justifies setting
a
= –
g
= –9.8 m/s
2
(taking
down
as
the –
y
direction) for the duration of the fall. This is constant acceleration motion, which
justifies the use of Table 21 (with
Δ
y
replacing
Δ
x
).
(a) Noting that
Δ
y
=
y
–
y
0
= –30 m, we apply Eq. 215 and the quadratic formula
(Appendix E) to compute
t
:
Δ
Δ
yv
t g
t
t
vvg
y
g
=−
¡
=
±−
0
2
00
2
1
2
2
which (with
v
0
= –12 m/s since it is downward) leads, upon choosing the positive root (so
that
t
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 Spring '06
 Stoler
 Physics, Resistance, Acceleration

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