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PROBLEM 17.142 (Continued)
22 2
1
Moments about C:
3
b
10
(3)(24)
10
9
PROBLEM 17.143
Disks A and B are made of the same material and are of the same thickness;
they can rotate freely about the vertical shaft. Disk B is at rest when it is
dropped onto disk A, which is rotating with an angular velocity of 500 rpm.
Knowing that disk A has a mass of 8 kg, determine (a) the final angular
velocity of the disks, (b) the change is kinetic energy of the system.
PROBLEM 17.143 (Continued)
(a) Final angular velocity of system:
2
(0.83505)(52.36)
PROBLEM 17.144
A square block of mass m is falling with a velocity
1
v
when it strikes a small
obstruction at B. Knowing that the coefficient of restitution for the impact between
corner A and the obstruction B is e 0.5, determine immediately after the impact
(a) the angular velocity of the block, (b) the velocity of its mass center G.
PROBLEM 17.144 (Continued)
Moments about A:
111 2
2
2
2
12
22
22
1
6
26 2 2
(1 ) 2
23
bbbb
mv I mev m
Imb
evb b
21
3(1 )
4ev
b
1
2
b
(b) Velocity of the mass center.
From Eq. (1),
21
vev
1
3(1 )
bev
PROBLEM 17.145
A 3-kg bar AB is attached by a pin at D to a 4-kg square plate, which can rotate
freely about a vertical axis. Knowing that the angular velocity of the plate is
120 rpm when the bar is vertical, determine (a) the angular velocity of the plate
after the bar has swung into a horizontal position and has come to rest against pin
C, (b) the energy lost during the plastic impact at C.
PROBLEM 17.146
A 1.8-lb javelin DE impacts a 10-lb slender rod ABC with a horizontal
velocity of v
0
30 ft/s as shown. Knowing that the javelin becomes
embedded into the end of the rod at Point C and does not penetrate very
far into it, determine immediately after the impact (a) the angular velocity
of the rod ABC after the impact, (b) the components of the reaction at B.
Assume that the javelin and the rod move as a single body after the
impact.
PROBLEM 17.146 (Continued)
Kinematics: (Rotation about B)
1
2
4.25 ft
AC
DE
vr
vr
where
22
12
22
2.5880 (0.31056)(3) 0.3365 (0.05590)(9.0588)
1.30167 rad/s
BAC AC DE DE
II mrI mr
1.302 rad/s
ω
Accelerations:
α
2
2
Free body and kinetic diagrams.
Moments about B:
412
22
2
() ()
0.74223 rad/s
DE AC AC AC t DE DE DE t
WrImarImar
2
0.742 rad/sα
PROBLEM 17.146 (Continued)
(b) Components of reaction at B.
:Fma
2
2
y
13.96 lb
y
B
PROBLEM 17.CQ1
A round object of mass m and radius r is released from rest at the top of a curved surface and rolls without
slipping until it leaves the surface with a horizontal velocity as shown. Will a solid sphere, a solid cylinder or
a hoop travel the greatest distance x?
(a) A solid sphere
(b) A solid cylinder
(c) A hoop
(d) They will all travel the same distance.
