Two charges, each of charge q, are separated by a distance d. The distance between the charges is doubled. If the original potential energy of the arrangement was 40 mJ, by how much does the potential energy change when the charges are moved to the increased distance?
a. It decreases by more than 20 mJ.
c. More information is needed. b. It decreases by less than 20 mJ
d. It decreases by 20 mJ.
Question 2
A railroad freight car, mass 15,000 kg, is allowed to coast along a level track at a speed of 2.0 m/s. It collides and couples with a 60,000-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. 20
c. 86
b. 23
d. 100
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