When charges qa, qb, and qc are placed respectively at the corners a, b, and c of a right triangle, the potential at the midpoint of the hypotenuse is 20 V. When the charge qa is removed, the potential at the midpoint becomes 15 V. When, instead, the charge qb is removed (qa and qc both in place), the potential at the midpoint becomes 12 V. What is the potential at the midpoint if only the charge
qc is removed from the array of charges?
a. 8.0 V
b. 5.0 V
c. 7.0 V
d. 13 V
d
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Which statement about the rotations of the Moon and Mercury is FALSE?
A) Our Moon is in a 1:1 synch with the Earth, keeping the same side toward us. B) Mercury is in the 3:2 synch with the Sun, with the same side Sunward at perihelion. C) Like our Moon, Mercury does not rotate at all, keeping the same side facing the Sun. D) On Mercury, three days exactly equal two years. E) On the Moon, each "day" lasts about 15 Earth days of constant sunlight.
A porch roof that slopes upward at 45° measures 3.0 m × 5.0 m. It is covered with a slab of insulating material that is 2.0 cm thick
If the density of the insulation is 15 kg/m3, what is the weight of the insulation, in pounds, on the roof? (1.00 kg weighs 2.2 lb and density is mass per unit volume.) A) 4.5 lb B) 9.0 lb C) 20 lb D) 990 lb E) 9.9 lb
Which of the following sound frequencies lie(s) outside the audible range?
a. 20 Hz b. 47 kHz c. 4300 Hz d. All of these
A light-emitting diode (LED) converts electricity to approximately sinusoidal electromagnetic waves with a definite frequency f. Imagine that light from the LED creates an oscillating electric field with amplitude E0 at a certain location. If we increase the electrical power to the LED so that the oscillation amplitude is now 2E0, by what factor have we increased the power?
A. 4 times
B. 2 times
C. 
times
D. One cannot answer without more information.