fisica1-youn-e-freedman-exercicios-resolvidos

6.58: The work per unit mass is ( W m)
= gh.
a) The man does work, ( 9.8 N kg) (0.4 m) = 3.92 J kg.
b) ( 3.92 J kg) (70 J kg) × 100 = 5.6%.
c) The child does work, ( 9.8 N kg) (0.2 m) = 1.96 J kg.
( 1.96 J kg) (70 J kg) × 100 = 2.8%.
d) If both the man and the child can do work at the rate of 70 J kg, and if the child
only needs to use 1 .96 J kg instead of 3 .92 J kg, the child should be able to do more pull
ups.
1
6.59: a) Moving a distance L along the ramp, s = L s = Lsin
α,
so IMA = .
in
,
out
b) If AMA = IMA, ( Fout
Fin
) = ( sin
sout
) and so ( F
out
) ( sout
) = ( Fin
) ( sin
) , or W
out
= W in
.
c)
sin α
d)
Wout
( Fout
)( sout
) Fout
Fin
E = = = =
W ( F )( s ) s s
in
in
in
in
out
AMA
.
IMA
3
w −Wg
s (7.35×
10 J)
6.60: a) m = = =
= 41.7 kg.
2
g g (9.80 m s ) (18.0 m)
3
W 8.25×
10 J
b) n = n =
458 N.
18.0 m
=
s
c) The weight is mg = Wg
s
= 408 N, so the acceleration is the net force divided by the
458 N − 408 N
2
mass, = 1.2 m s .
41.7 kg
6.61: a)
2
2
1 12
6
2 1 ⎛ 2πR
⎞ 1 ⎛ 2π(6.66
× 10 m) ⎞
mv = m⎜
⎟ = (86,400 kg)
= 2.59×
10
2 2
2
⎜
(90.1min) (60 s min)
⎟
⎝ T ⎠
⎝
⎠
2
2
3
b) (1 2) mv = (1 2) (86,400 kg) ((1.00 m) (3.00 s)) = 4.80 × 10 J.
J.