Which of the following best describes the relationship between two systems in thermal equilibrium? a. no net energy is exchanged. c. the masses are equal. b. the volumes are equal. d. the velocity is zero.

Ibelieve that the correct answer is: c. along plate boundaries

Distance covered = speed x timethe distance traveled going against the stream = distance traveled with the stream.therefore it is the speed and the time that are the variables.as he travels the same distance both ways, speed x time is the same for each way.going upstream his speed is 4 kph; going downstream his speed is 6 kph.therefore we have two simultaneous equations: time upstream x 4 = time downstream x 6time upstream + time downstream = 60 minutestherefore we have the equation: time upstream = 6/10 hour, time downstream therefore = 4/10 hour.distance traveled at 4km/hr in 6/10 hour = 24/10 = 2.4km.check: distance traveled at 6km/hr in 4/10 hour = 24/10 = 2.4km.

Mass and velocity are the 2 factors used to calculate kinetic energy. the equation for kinetic energy is (1/2)mv^2. hope this !