A 25 kg child plays on a swing with support ropes that are 2.2 m long. A friend pulls her back until the ropes are 42.2 from the vertical and releases her from rest. What is the potential
energy for the child just as she is released compared with the potential energy at the bottom of
the swing?
A. 177 J
B. 140 J
O
C. 539 J
D. 160 J

How would you place two electrons on a sphere of radius r so that the electrostatic potential energy is minimized. how would you place three electrons to solve the same problem.

Acoal-fired plant generates 600 mw of electric power. the plant uses 4.8 x 10^6 kg of coal each day, and the heat of combustion of coal is 3.3x 10^7 j/kg. the steam that drives the turbines is at a temperature of 300° c, and the exhaust water is at 37° c. (a) what is the overall efficiency of the plant for generating electric power? (b) how much thermal energy is exhausted each day? (c) what is the change in entropy of the universe for this heat engine? (d) using the same heat reservoirs, what is the maximum possible (carnot) efficiency for a heat engine?

Compare the horizontal displacement of the two balls as they travel to the ground. what do you observe?