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1. (a) Noting that the vertical displacement is 10.0 m – 1.50 m = 8.50 m downward (same
direction as
G
F
g
), Eq. 712 yields
2
cos
(2.00 kg)(9.80 m/s )(8.50 m)cos0
167 J.
g
Wm
g
d
φ
==
°
=
(b) One approach (which is fairly trivial) is to use Eq. 81, but we feel it is instructive to
instead calculate this as
Δ
U
where
U
=
mgy
(with upwards understood to be the +
y
direction). The result is
2
(
)
(2.00 kg)(9.80 m/s )(1.50 m 10.0 m)
167 J.
fi
Um
g
y y
Δ=
− =
−
=
−
(c) In part (b) we used the fact that
U
i
=
mgy
i
=196 J.
(d) In part (b), we also used the fact
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 Spring '08
 Any
 Physics

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