A charge of +80 ?C is placed on the x axis at x = 0 . A second charge of ?50 ?C is placed on the x axis at x = 50 cm. What is the magnitude of the electrostatic force on a third charge of 4.0 ?C placed on the x axis at x = 30 cm?
a. 13 N
b. 77 N
c. 39 N
d. 25 N
e. 45 N
b
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You can reason that the time required for a ball to fall is related to the height from which it falls and to the acceleration due to gravity. Time is measured in seconds, height in meters, and gravitational acceleration. Using dimensional analysis, determine how the time to fall from height h compares to the time required to fall from height 2h.
A. It takes 1/2 as long
B. It takes 4 times as long
C. It takes 
times as long
D. It takes 2 times as long
E. It takes 
as long
F. It takes 1/4 as long
Hydrogen gas seems to have a diffusivity of about 2.6 x 10^-13 m^2/s when diffusing into iron at 770 K. What would you expect the rate of diffusion or mass flow rate per unit area of hydrogen to be when stored in an iron container at 5 atmospheres pressure, assuming the density of hydrogen at 1 mm in the iron from the containing surface to be 5% of the normal hydrogen density, given by p/RT?
What will be an ideal response?
A large billet of steel initially at 260°C is placed in a radiant furnace where the surface temperature is held at 1200°C. Assuming the billet to be infinite in extent, compute the temperature at point P shown in the accompanying sketch after 25 min have elapsed. The average properties of steel are: k = 28 W/(m K), p = 7360 kg/m3, and c = 500 J/(kg K).
GIVEN
FIND
The temperature at point P shown in the accompanying sketch
ASSUMPTIONS
The billet infinite in extent
SKETCH
A sled having a certain initial speed on a horizontal surface comes to rest after traveling 10 m. If the coefficient of kinetic friction between the object and the surface is 0.20, what was the initial speed of the object?
A) 9.8 m/s B) 6.3 m/s C) 3.6 m/s D) 7.2 m/s E) 8.9 m/s