Homework No. 13
Work and power in rotation
Y&F
10.32
Ans
: (a) 46.2 rad/s
2
(b) 53.9 rad/s (c) 61.3 kJ (d) 52.6 kW (e) 105 kW
Note
: Treat the propeller as a slender rod pivoted at its center.
O
R
= 0.4 m
L
= 0.6 m
Energy equation including rigid body rotation
CHANG
1
An 8 Kg slender rod and a small 4 Kg
sphere are mounted on a 15 Kg disk. The assembly is
released from rest at the horizontal position shown.
Find the angular velocity of the assembly when it
rotates 90° down to the vertical position.
Ans
: 5.11 rad/s
CHANG
2
The 10 Kg block is attached to a
spring (k = 100 N/m) and a cord that wraps
around the pulley as shown. The block
slides on the tabletop (
μ
= 0.4) as a
constant torque
τ
= 25 Nm is applied to
turn the pulley from rest. The pulley
(radius
R
= 0.1 m, moment of inertia
I
=
0.24 Kgm2) is pivoted at the center and the
spring is initially unstretched. Fin
k
d the

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