Chapter 12: Q.39 (page 332)
Vector and vector . What is the cross product ?
Short Answer
The cross product of the vectors and is .
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Chapter 12: Q.39 (page 332)
Vector and vector . What is the cross product ?
The cross product of the vectors and is .
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Evaluate the cross products and

In FIGURE CP12.88, a 200 g toy car is placed on a narrow 60-cm-diameter track with wheel grooves that keep the car going in a circle. The 1.0 kg track is free to turn on a frictionless, vertical axis. The spokes have negligible mass. After the car鈥檚 switch is turned on, it soon reaches a steady speed of 0.75 m/s relative to the track. What then is the track鈥檚 angular velocity, in rpm?

An object whose moment of inertia is experiences the torque shown in FIGURE EX12.25. What is the object's angular velocity at ? Assume it starts from rest.

During most of its lifetime, a star maintains an equilibrium size in which the inward force of gravity on each atom is balanced by an outward pressure force due to the heat of the nuclear reactions in the core. But after all the hydrogen 鈥渇uel鈥 is consumed by nuclear fusion, the pressure force drops and the star undergoes a gravitational collapse
until it becomes a neutron star. In a neutron star, the electrons and protons of the atoms are squeezed together by gravity until they fuse into neutrons. Neutron stars spin very rapidly and emit intense pulses of radio and light waves, one pulse per rotation. These 鈥減ulsing
stars鈥 were discovered in the 1960s and are called pulsars.
a. A star with the mass M = 2.0 x 1030 kg and size R =7.0 x 108 m of our sun rotates once every 30 days. After undergoing gravitational collapse, the star forms a pulsar that is observed by astronomers to emit radio pulses every 0.10 s. By treating the neutron star as a solid sphere, deduce its radius.
b. What is the speed of a point on the equator of the neutron star? Your answers will be somewhat too large because a star cannot be accurately modeled as a solid sphere. Even so, you will be able to show that a star, whose mass is 106larger than the earth鈥檚, can be compressed by gravitational forces to a size smaller than a typical state in the United States!
A 10 g bullet traveling at 400 m/s strikes a 10 kg, 1.0-m-wide door at the edge opposite the hinge. The bullet embeds itself in the door, causing the door to swing open. What is the angular velocity of the door just after impact?
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