fisica1-youn-e-freedman-exercicios-resolvidos

3.20: a) If air resistance is to be ignored, the components of acceleration are 0
2
horizontally and − g = −9.80 m s vertically.
b) The x-component of velocity is constant at v = ( 12.0 m s)cos51.0°
= 7.55 m s . The
y-component is v = (12.0 m s)sin 51.0°
9.32 m s at release and
0 y
=
2
0
−
v y
− gt = (10.57 m s) − (9.80 m s )(2.08 s) = 11.06 m s when the shot hits.
c) v0 x
t = (7.55 m s)(2.08 s) = 15.
7 m .
d) The initial and final heights are not the same.
e) With y = 0 and v 0y as found above, solving Eq. (3.18) for y = 1.81
0
m .
x
f)
3.21: a) The time the quarter is in the air is the horizontal distance divided by the
horizontal component of velocity. Using this time in Eq. (3.18),
2
x gx
y − y0
= v0
y
−
2
v 2v
0x
= tanα
0
x −
v
2
0
0x
2
gx
2
2cos α
0
2
2
(9.80 m s )(2.1 m)
= tan 60°
(2.1m) −
= 1.53 m rounded.
2 2
2(6.4 m s) cos 60°
b) Using the same expression for the time in terms of the horizontal distance in
Eq. (3.17),
2
gx
(9.80 m s )(2.1 m)
v y
= v0 sinα
0
− = (6.4 m s)sin 60° −
= −0.89 m s.
v cosα
(6.4 m s)cos60°
0
0