A 60-mC charge is held fixed at the origin and a -20-mC charge is held fixed on the x axis at a point x = 1.0 m. If a 10-mC charge is released from rest at a point x = 40 cm, what is its kinetic energy the instant it passes the point x = 70 cm?
a. 9.8 J
b. 7.8 J
c. 8.8 J
d. 6.9 J
e. 2.8 J
C
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What made Maxwell's equations conflict with Galilean invariance while Newton's laws did not conflict?
a. They depended on acceleration rather than velocity. b. They depended on velocity rather than acceleration. c. They dealt with non-inertial systems rather than inertial systems. d. They dealt with inertial systems rather than non-inertial systems. e. They dealt with electromagnetic effects rather than mechanics.
A student has to work the following problem: A block is being pulled along at constant speed on a horizontal surface a distance d by a rope supplying a force F at an angle of elevation q. The surface has a frictional force acting during this motion. How much work was done by friction during this motion? The student calculates the value to be –Fdsinq. How does this value compare to the correct
value? a. It is the correct value. b. It is too high. c. It is too low. d. The answer cannot be found until it is known whether q is greater than, less than, or equal to 45°.
A light source radiates 60.0 W of single-wavelength sinusoidal light uniformly in all directions. What is the amplitude of the magnetic field of this light at a distance of 0.700 m from the bulb?
(?0 = 8.85 × 10-12 C2/N ? m2, ?0 = 4? × 10-7 T ? m/A, c = 3.0 × 108 m/s) A) 1.76 × 10-7 T B) 2.02 × 10-7 T C) 2.22 × 10-7 T D) 2.86 × 10-7 T
In Figure 7.4, the time for the fraction of residual strain in iron to drop to 0.6 at 400°C is 137 minutes, and at 450°C it is 15 minutes.
(a) Calculate the activation enthalpy for the recovery of cold work in iron. (b) Comment on the magnitude of the activation enthalpy for recovery in comparison to the activation enthalpy for vacancy diffusion in iron, and justify your result.