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PROBLEM 17.123
A slender rod AB is released from rest in the position shown. It
swings down to a vertical position and strikes a second and
identical rod CD which is resting on a frictionless surface.
Assuming that the coefficient of restitution between the rods is
0.4, determine the velocity of rod CD immediately after the
impact.
PROBLEM 17.123 (Continued)
Principle of impulse-momentum at impact.
2
Syst Momenta 23
Syst Ext Imp
3
Syst Momenta
LL
44 4
110.43
PROBLEM 17.124
A slender rod AB is released from rest in the position shown. It
swings down to a vertical position and strikes a second and
identical rod CD which is resting on a frictionless surface.
Assuming that the impact between the rods is perfectly elastic,
determine the velocity of rod CD immediately after the impact.
PROBLEM 17.124 (Continued)
Impact condition:
32
3
CB B
vvev
2 2 12 2 2 12
LL
g
For perfectly elastic impact, 1.e
3
4
C
vgL
30.866
C
g
Lv
PROBLEM 17.125
Block A of mass m is attached to a cord which is wrapped around a uniform disk of mass
M. The block is released from rest and falls through a distance h before the cord becomes
taut. Derive expressions for the velocity of the block and the angular velocity of the disk
immediately after the impact. Assume that the impact is (a) perfectly plastic, (b) perfectly
elastic.
PROBLEM 17.125 (Continued)
Substituting (4) into (2) and using (1) for v1
2121
1
2
mv M v v mv
2
mM
mM
PROBLEM 17.126
A 2-kg solid sphere of radius r 40 mm is
dropped from a height h 200 mm and lands on
a uniform slender plank AB of mass 4 kg and
length L 500 mm which is held by two
inextensible cords. Knowing that the impact is
perfectly plastic and that the sphere remains
attached to the plank at a distance a 40 mm
from the left end, determine the velocity of the
sphere immediately after impact. Neglect the
thickness of the plank.
PROBLEM 17.126 (Continued)
Kinematics.
To locate the instantaneous center C
draw line
AC
perpendicular to
v
A
and
(0.500 m)cos30 0.040 m
0.47301m
22
0.21m
2
0.51753 m
L
HS a
CS CH HS
HS
Principle of impulse and momentum.
Syst. Momenta
1
Syst. Ext. Imp.
1
2
Syst. Momenta
2
Moments about C:
2
2
0() ()
2
2
S S S S AB G S AB
mv a mv CS m v CH I I
L
PROBLEM 17.126 (Continued)
2
L
22
(0.53567 0.75 0.00128 0.08333) kg m 1.37028 kg m
22
0.83198 kg m /s (1.37028 kg m )
0.60716 rad/s
ω
1
(0.51753 m)(0.60716 rad/s) 0.31422 m/s
S
v
1
1
3()[ sin]/cos30
27.9236 (2)(0.31422)sin 23.94
SS S
SS S
Adt Bdt m v m v
21.6260 N s
Adt Bdt
Solving the simultaneous equation gives
6.05 N s 2.80 N sAdt Bdt
PROBLEM 17.127
Member ABC has a mass of 2.4 kg and is attached to a pin support
at B. An 800-g sphere D strikes the end of member ABC with a
vertical velocity
1
v
of 3 m/s. Knowing that
750L
mm and that
the coefficient of restitution between the sphere and member ABC
is 0.5, determine immediately after the impact (a) the angular
velocity of member ABC, (b) the velocity of the sphere.
