104. We note that
F
N
=
mg
in this situation, so
f
k
=
μ
k
mg
= (0.32) (220 N) = 70.4 N and
f
s
,max
=
s
mg
= (0.41) (220 N) = 90.2 N.
(a) The person needs to push at least as hard as the static friction maximum if he hopes to
start it moving. Denoting his force as
P
, this means a value of
P
slightly larger than
90.2 N is sufficient. Rounding to two figures, we obtain
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 Spring '08
 Any
 Physics, Force, Friction

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