Length Contraction: When an object moves close to the speed of light relative to Earth, what happens to its dimensions compared to what they were before it began moving, as measured by an Earth-based observer?
A. Only lengths parallel to the direction of travel are decreased.
B. Only lengths perpendicular to the direction of travel are decreased.
C. All lengths are decreased.
D. No lengths are affected.
Answer: A
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Two long parallel wires carry currents of 20 A and 5.0 A in opposite directions. The wires are separated by 0.20 m. What is the strength of the magnetic field midway between the two wires? (?0 = 4? × 10-7 T ? m/
A) A) 1.0 × 10-5 T B) 2.0 × 10-5 T C) 3.0 × 10-5 T D) 4.0 × 10-5 T E) 5.0 × 10-5 T
An airplane has a mass of 8,000 kg and is flying at 150 m/s in level flight. The airplane drops 1,000 kg of water on a fire below. The velocity of the airplane after dropping the water is
A. 50 m/s. B. 60 m/s. C. 75 m/s. D. 100 m/s. E. 150 m/s.
The work that a force does by acting on an object is equal to:
a. the product of force (in the direction of motion) and distance and is positive if the force and motion are in the same direction. b. the product of force (in the direction of motion) and distance and is negative if the force and motion are in the same direction. c. the product of force and distance without regard to direction. d. the product of momentum and force (in the direction of motion). e. the product of distance and kinetic energy.
The apparent size of an object based on the amount of sky it covers is called its ________.
A. shadow-width B. diameter C. angular size D. horizon E. celestial extent