fisica1-youn-e-freedman-exercicios-resolvidos

5.28: a) The stopping distance is
2 2
2
v v (28.7 m s)
= =
= 53 m.
2
2a
2µ
kg
2(0.80) (9.80 m s )
b) The stopping distance is inversely proportional to the coefficient of friction and
proportional to the square of the speed, so to stop in the same distance the initial speed
should not exceed
v
µ
µ
k, wet
k,dry
= (28.7 m s)
0.25
0.80
== 16
m s.
5.29: For a given initial speed, the distance traveled is inversely proportional to the
0 .44
coefficient of kinetic friction. From Table 5.1, the ratio of the distances is then = 11.
0.04
5.30: (a) If the block descends at constant speed, the tension in the connecting string
must be equal to the hanging block’s weight, w
B.
Therefore, the friction force µ w k A
on
block A must be equal to w
B,
and w
B
= µ
kwA.
(b) With the cat on board, a = g w − µ 2w
) ( w + 2w
).
(
B k A B A
5.31:
a) For the blocks to have no acceleration, each is subject to zero net force. Considering
the horizontal components,
r
T = f
A,
F = T + fB,
or
r
F = f + f .
Using
f
A
= µ
kgmA
and fB
µ
kgmB
b) T = f A
= µ gm .
k
A
A
B
= gives F r = µ g ( m A
+ m ) .
k
B