A roofer lifts supplies a height of 20. m with a hand-operated winch. How long would it take him to lift a 200. kg load, if the winch has an efficiency of 90%, and the rate at which the winch can do work is 0.80 hp?
What will be an ideal response?
73. seconds
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A 50. ? resistor is placed in series with a 40. mH inductor. At what frequency will the current in such a circuit lag the applied voltage by exactly 45°?
What will be an ideal response?
None of the pulsars emit pulses of visible light because
a. pulsars are too hot to emit visible light. b. pulsars contain black holes that won't let visible light escape. c. the gravitational field of a pulsar is so great that the visible light emitted is redshifted. d. pulsars are too far away for the visible light to be bright enough to be detected at Earth. e. A few pulsars do emit visible light pulses.
Carnot Engine: An inventor tries to sell you his new heat engine that takes in 40 J of heat at 87°C on each cycle, expels 30 J at 27°C, and does 10 J of work. Would it be wise to invest in this engine? Back up your conclusion with numerical calculations.
What will be an ideal response?
As the moon circles Earth, the net force on it is
A) backward. B) directed outward away from Earth. C) directed inward toward Earth. D) forward. E) zero.