I
Givens Solutions
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Section One—Student Edition SolutionsV Apx I–33
189.m
1=7.00 kg
v
1, i=2.00 m/s to the east
(at 0°)
m
2=7.00 kg
v
1, i=0 m/s
v
1, f=1.73 m/s at 30.0°
north of east
Momentum conservation
In the x-direction:
m
1v
1, i (cos q
1, i) +m
2v
2, i (cos q
2, i) =m
1v
1, f(cos q
1, f) +m
2v
2, f(cos q
2, f)
v
2, f(cos q
2, f) =v
1, i (cos q
1, i) +v
2, i (cos q
2, i) −v
i, f(cos q
1, f)
v
2, f(cos q
2, f) =(2.00 m/s)(cos 0°) +0 m/s −(1.73 m/s)(cos 30.0°)
v
2, f=2.00 m/s −1.50 m/s =0.50 m/s
In the y-direction:
m
1v
1, i (sin q
1, i) +m
2v
2, i (sin q
2, i) =m
1v
1, f(sin q
1, i) m
2v
2, f(sin q
2, f)
v
2, f(sin q
2, f) =v
1, i (sin q
1, i) +v
2, i (sin q
2, i) −v
2, f(sin q
2, f)
v
2, f(sin q
2, f) =(2.00 m/s)(sin 0°) +0 m/s −(1.73 m/s)(sin 30.0°) =−0.865 m/s
=
tan q
2, f=−1.7
q
2, f=tan
−1
(−1.7) =(−6.0 ×10
1
)°
v
2, f= = 1.0 m/s
v
2, f=
Conservation of kinetic energy (check)
1
2
m
1v
1, i
2+
1
2
m
2v
2, i
2=
1
2
m
iv
1, f
2+
1
2
m
2v
2, f
2
1
2
(7.00 kg)(2.00 m/s)
2
+
1
2
(7.00 kg)(0 m/s)
2
=
1
2
(7.00 kg)(1.73 m/s)
2
+
1
2
(7.00 kg)(1.0 m/s)
2
14.0 J +0 J =10.5 J +3.5 J
14.0 J =14.0 J
1.0 m/s at (6.0 ×10
1
)°south of east
0.50 m/s
cos(−6.0 ×10
1
)°
−0.865 m/s
0.50 m/s
v
2, f(sin q
2, f)
v
2, f(cos q
2, f)
190.m
1=2.0 kg
v
1, i=8.0 m/s
v
2, i=0 m/s
v
1, f=2.0 m/s
m
1v
1, i+m
2v
2, i=m
1v
1, f+m
2v
2, f
1
2
m
1v
1, i
2+
1
2
m
2v
2, i
2=
1
2
m
1v
1, f
2+
1
2
m
2v
2, f
2
m
2=
1
2
m
1v
1, i
2+
1
2
E2
v
2, i
2=
1
2
m
1v
1, f
2+
1
2
v=
v
2, f
2
v
1, i
2(v
2, i-v
2, f) +(v
1, f-v
1, i)v
2, i
2=v
1, f
2(v
2, i-v
2, f) +(v
1, f-v
1, i)v
2, f
2
(v
1, i
2v
2, i+v
1, fv
2, i
2-v
1, iv
2, i
2-v
1, f
2v
2, i+v
2, f(v
1, f
2-v
1, i
2) =v
2, f
2(v
1, f-v
1, i)
Because v
2, i=0, the above equation simplifies to
v
1, f
2−v
1, i
2=v
2, f(v
1, f−v
1, i)
v
2, f=v
1, f+v
1, i=2.0 m/s +8.0 m/s =10.0 m/s
m
2= = =
m
2=1.2 kg
−12 kg•m/s
−10.0 m/s
4.0 kg
•m/s −16 kg •m/s
−10.0 m/s
(2.0 kg)(2.0 m/s) −(2.0 m/s)(8.0 m/s)
0 m/s −10.0 m/s
m
1v
1, f−m
1v
1, i
v
2, i−v
2, f
m
1v
1, f−m
1v
1, i
v
2, i−v
2, f
m
1v
1, f−m
1v
1, i
v
2, i−v
2, f