An object falling from a great height in Earth's atmosphere eventually reaches a speed called Terminal velocity. What cause a falling object to stop increasing in speed once it reaches terminal velocity? Really struggling, I need an answer--quick. Which letter is correct and why please? A. Its mass and weight have become equal
B. It has no more potential energy
C. No forces are acting on it any longer
D. The forces acting on it are balanced

Two kilograms of air within a piston–cylinder assembly executes a carnot power cycle with maximum and minimum temperatures of 800 k and 300 k, respectively. the heat transfer to the air during the isothermal expansion is 60 kj. at the end of the isothermal expansion the volume is 0.4 m3. assume the ideal gas model for the air. determine the thermal efficiency, the volume at the beginning of the isothermal expansion, in m3, and the work during the adiabatic expansion, in kj.