1.Knight 13.069. [455110]Show Details
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10
The 1.6 kg, 40 cm diameter disk in Figure P13.69 is spinning at 280 rpm. How much friction force must the brake apply to the rim to bring the disk to a halt in 3.5 s?
[1.34] N
Figure P13.69
2.Knight 13.061. [492877]Show Details
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A 0.9 kg mass at (x, y) = (20 cm, 20 cm) and a 2.0 kg mass at (20 cm, 100 cm) are connected by a massless, rigid rod. They rotate about the center of mass.
(a) What are the coordinates of the center of mass?
( [20] cm, [75.2] cm)
(b) What is the moment of inertia about the center of mass?
[0.397] kgm2
(c) What constant torque will cause an angular velocity of 6.25 rad/s at the end of 3.0 s, starting from rest?
[0.828] Nm
(d) At what angle, with respect to the axis of the rod, should 1.2 N forces be applied to each mass to give the torque you found in part c?
[59.5]°
3.Knight 13.056. [380253]Show Details
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A 3.0 m long rigid beam with a mass of 115 kg is supported at each end. An 65 kg student stands 2.0 m from support 1. How much upward force does each support exert on the beam?
right support / [988] Nleft support / [776] N
Figure Ex13.56
4.Knight 13.041. [380251]Show Details
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3.33
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Force = -12N is exerted on a particle at = (8+ 5 ) m. What is the torque on the particle about the origin?
( [0]+ [0]+ [-96]) Nm
5.Knight 13.029. [380276]Show Details
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The three 200 g masses in Figure Ex13.29 are connected by massless, rigid rods to form a triangle. What is the triangle's rotational kinetic energy if it rotates at 5.0 rev/s about an axis through the center?
[15.8] J
Figure Ex13.29
6.Knight 13.018. [492881]Show Details
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The four masses shown in Figure Ex13.17 are connected by massless, rigid rods, with m = 189 g.
(a) Find the coordinates of the center of mass.
( [5.65] cm, [5.65] cm)
(b) Find the moment of inertia about a diagonal axis that passes through masses B and D.
[14.4] kgcm2
7.Knight 13.014. [380274]Show Details
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The 26 cm diameter disk in Figure Ex13.14 can rotate on an axle through its center. What is the net torque about the axle if F = 16 N?
[2.04] Nm [ clockwise ]
Figure Ex13.14
8.Knight 13.067. [545217]Show Details
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The two blocks, m1 = 3.1 kg and m2 = 4.3, in the figure below are connected by a massless rope that passes over a pulley. The pulley is 12 cm in diameter and has a mass of 2.0 kg. As the pulley turns, friction at the axle exerts a torque of magnitude 0.50 Nm. If the blocks are released from rest, how long does it take the 4.3 kg block to reach the floor from a height of h = 1.0 m?
[2.21] s
9.Knight 13.006. [455093]Show Details
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A magnetic computer disk 10.0 cm in diameter is initially at rest. A small dot is painted on the edge of the disk. The disk accelerates at 660 rad/s2 for 1/2 s, then coasts at a steady angular velocity for another 1/5 s. What is the speed of the dot at t = 0.70 s?
[16.5]m/s
Through how many revolutions has it turned?
[23.6] rev
10.Knight 13.032. [380219]Show Details
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A car tire is 64 cm in diameter. The car is traveling at a speed of 20 m/s.
(a) What is the tire's rotation frequency, in rpm?
[597] rpm
(b) What is the speed of a point at the top edge of the tire?
[40] m/s
(c) What is the speed of a point at the bottom edge of the tire?
[0] m/s