fisica1-youn-e-freedman-exercicios-resolvidos

8.31: Use conservation of the horizontal component of momentum to find the velocity of
the combined object after the collision. Let +x be south.
P x
is constant gives
(0.250 kg)(0.200 m s) − (0.150 kg)(0.600 s) = (0.400 kg) v
v
2x
K
K
1
2
= −10.0 cm s ( v
=
=
1
2
1
2
∆K
= K
(0.250 kg)(0.200 s)
(0.400 kg)(0.100 s)
2
− K
1
2
= 10.0 cm s, north)
2
= −0.0300 J
2
+
1
2
(0.150 kg)(0.600 s)
= 0.0020 J
2
2x
= 0.0320 J
Kinetic energy is converted to thermal energy due to work done by
nonconservative forces during the collision.
8.32: (a) Momentum conservation tells us that both cars have the same change in
momentum, but the smaller car has a greater velocity change because it has a smaller
mass.
M∆V
= m∆v
M
∆v
(small car) = ∆V
(large car)
m
3000 kg
= ∆V
= 2.5∆V (large car)
1200 kg
(b) The occupants of the small car experience 2.5 times the velocity change of
those in the large car, so they also experience 2.5 times the acceleration. Therefore they
feel 2.5 times the force, which causes whiplash and other serious injuries.
8.33: Take east to be the x-direction and north to be the y-direction (again, these choices
are arbitrary). The components of the common velocity after the collision are
v x
v
y
(1400 kg) ( −35.0
km h)
=
= −11.67
km
(4200 kg)
(2800 kg) ( −50.0 km h)
=
= −33.33
km
(4200 kg)
h
h.
The velocity has magnitude ( −11.67 km
− .33
direction arctan ( ) = 70. 7°
h)
33
south of west.
−11.67
2
+ ( −33.33 km
h)
2
= 35.3
km
h and is at a