A 5.0-kg mass is suspended by a string from the ceiling of an elevator that is moving upward with a speed which is decreasing at a constant rate of 2.0 m/s in each second. What is the tension in the string supporting the mass?
a. 49 N
b. 39 N
c. 59 N
d. 10 N
e. 42 N
b
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A filament of tungsten wire is 0.001 m in diameter, and the filament is heated to 2500 K. The work function of tungsten is 4.5 eV.
(a) Calculate the probability of electrons having sufficient energy to be emitted from the filament. (b) Calculate the emission current density from the tungsten wire. (c) What length of wire can produce a thermionic electron current of 1 A?
There is a temperature at which the reading on the Kelvin scale is numerically:
A. equal to that on the Celsius scale B. lower than that on the Celsius scale C. equal to that on the Fahrenheit scale D. less than zero E. none of the above
In some regions of the corona, the magnetic field does not loop back to the Sun, and the gas escapes unimpeded. These regions are called _______ and are believed to be the source of the solar wind
a. prominences b. flares c. granules d. auroras e. coronal holes
Why are astronauts weightless in the Space Station?
A) because the Space Station is traveling so fast B) because the Space Station is constantly in free-fall around the Earth C) because there is no gravity in space D) because the Space Station is moving at constant velocity