fisica1-youn-e-freedman-exercicios-resolvidos

4.43:
a) The engine is pulling four cars, and so the force that the engine exerts on the first car
is 4 m a r . b), c), d): Similarly, the forces the cars exert on the car behind are
r r
3 m a , 2m a and − m a r . e) The direction of the acceleration, and hence the direction of
the forces, would change but the magnitudes would not; the answers are the same.
4.44: a) If the gymnast climbs at a constant rate, there is no net force on the gymnast, so
the tension must equal the weight; T = mg .
b) No motion is no acceleration, so the tension is again the gymnast’s weight.
c) T − w = T − mg = ma = m a r (the acceleration is upward, the same direction as the
tension), so T = m( g + a r ) .
d) T − w = T − mg = ma = −m
a r (the acceleration is downward, the same opposite as
the tension), so T = m( g − a r ) .
4.45: a)
The maximum acceleration would occur when the tension in the cables is a maximum,
a
F
m
T − mg
m
T
m
net
= = = − g
=
28 ,000 N
2
− 9.80 m / s = 2.93 m / s
2 .
2200 kg
28,000 N
2
b) − 1.62 m /s
2 = 11.1m /s .
2200 kg