The following statements all refer to the human brain when mental activity is occurring. Which statement is correct?
a. In order to detect electric currents in the brain, you must open the skull and make direct electrical contact with the brain.
b. The electric currents in the brain can be detected outside the brain by detecting the magnetic fields they produce. c. The electric currents in the brain can be mapped by shaving a person's head and dropping iron filings on the head. d. The electric currents in the brain produce an aura that can be detected visually.
e. The electric currents in the brain cannot be detected by any means.
B
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What is aerobraking?
A) the technique of using a planetary atmosphere to change the orbit of a spacecraft B) the use of a planetary atmosphere to redirect a spacecraft to another planet C) the controlled landing of a spacecraft on a planetary surface D) the gradual decrease of speed as a spacecraft leaves the solar system E) the destruction of a spacecraft by the intense pressure as it descends into the atmosphere
The velocity of a particle (m = 10 mg, q = ?4.0 ?C) at t = 0 is 20 m/s in the positive x direction. If the particle moves in a uniform electric field of 20 N/C in the positive x direction, what is the particle's speed at t = 5.0 s?
a. 60 m/s b. 20 m/s c. 45 m/s d. 40 m/s e. 70 m/s
Jill does twice as much work as Jack does and in half the time. Jill's power output is
A) the same as Jack's power output. B) one-fourth as much as Jack's power output. C) one-half as much as Jack's power output. D) twice Jack's power output. E) four times Jack's power output.
A railroad freight car, mass 15 000 kg, is allowed to coast along a level track at a speed of 3.0 m/s. It collides and couples with a 54 000-kg loaded second car, initially at rest and with brakes released. What percentage of the initial kinetic energy of the 15 000-kg car is preserved in the two-coupled cars after collision?
a. 78% b. 22% c. 18% d. 38% e. 14%