Identical point charges (+20 ?C) are placed at the corners of an equilateral triangle with sides of 2.0-m length. How much external energy is required to bring a charge of 45 ?C from infinity to the midpoint of one side of the triangle?
a. 26 J
b. 16 J
c. 23 J
d. 21 J
e. 12 J
d
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What distance method is used to determine the distance to the most distant galaxies?
a. Radar echo b. Supernova observations c. Period-luminosity relationship of variable stars d. Parallax
You can be certain that a collision between two objects is elastic if
A. The system’s total momentum is conserved. B. The system’s total energy is conserved. C. The system’s total kinetic energy is conserved. D. If the objects are bouncy or springy. E. If the objects stick together after the collision.
The potential energy of a spring is 0.3 J when it is compressed 0.04 m to the left of its equilibrium position. This is its leftmost position. What is its kinetic energy at this point?
A. 375 N/m B. -0.3 J C. zero D. 0.3 J
The diagram below shows the position of a long straight wire perpendicular to the page and a set of directions labeled A through H. When the current in the wire is directed up out of the page, the direction of the magnetic field at point P is
a.
D.
b.
E.
c.
F.
d.
G.
e.
H.