Power: The power factor of an ac RL circuit with a 100-? resistor and a certain inductor is 0.60. What is the impedance of the circuit?
A. 170 ?
B. 85 ?
C. 340 ?
D. 100 ?
E. 60 ?
Answer: A
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A 50-kg satellite circles the Earth in an orbit with a period of 120 min. What minimum energy is required to change the orbit to another circular orbit with a period of 180 min? (Earth: radius = 6.4 × 10^6 m, mass = 6.0 × 10^24 kg)
a. 2.9 × 10^8 J b. 3.5 × 10^8 J c. 4.1 × 10^8 J d. 4.7 × 10^8 J e. 5.9 × 10^8 J
A certain aircraft has a mass of 300,000 kg. At a certain instant during its landing, its speed is 27.0 m/s. If the braking force is a constant 445,000 N, what is the speed of the airplane 10.0 s later?
A) 10.0 m/s B) 12.2 m/s C) 14.0 m/s D) 18.0 m/s E) 20.0 m/s
Electrons are collected by removing them from the atoms in a sample of water vapor (H2O, molecular mass 18u). If every hydrogen atom has lost an electron in the process, what is the mass of the sample if a charge of exactly 1.0C was collected?
A. 62 ?g B. 370 ?g C. 93 ?g D. 180 ?g
If we say that a galaxy has a lookback time of 1 billion years, we mean that
A) its light traveled through space for 1 billion years to reach us. B) is now 1 billion light-years away. C) it was 1 billion light-years away when the light left the galaxy. D) it is 400 million years old.