fisica1-youn-e-freedman-exercicios-resolvidos

5.65: a) The instrument has mass m = w g = 1.531kg
. Forces on the instrument:
v
0 y
v
y
= 0, v
= v
0 y
y
= 330 m s, a
+ a t gives t = 25.3 s
y
y
∑ F
y
= ma
T − mg = ma
T − mg
a = = 13.07 m
m
2
= 13.07 m s , t = ?
Consider forces on the rocket; rocket has the same a
y
. Let F be the thrust of the
rocket engines.
F − mg = ma
F = m(
g + a)
=
(25,000 kg) (9.80
1 2
b) y − y0 = v0
y
t + ayt
gives y − y0
= 4170 m.
2
m
s
2
y
2
s
2
5
+ 13.07 m s ) = 5.72×
10 N
5.66: The elevator’s acceleration is:
dv( t)
2
3
2
3
a = = 3.0 m s + 2(0.20 m s ) t = 3.0 m s + (0.40 m s ) t
dt
2
3
2
At t = 4 .0 s, a = 3.0 m s + (0.40 m s )(4.0 s) = 4.6 m s . From Newton’s Second Law,
the net force on you is
F = F − w = ma
F
net
scale
scale
2
2
= apparent weight = w + ma = (72 kg)(9.8 m s ) + (72 kg)(4.6 m s )
= 1036.8
N or 1040
N