What is true about the direction of the force of friction? A. It always points straight down. B. It always opposes the direction of motion. C. It always points straight up. D. It never changes direction.​

An ideal otto cycle has a compression ratio of 10.5, takes in air at 90 kpa and 40°c, and is repeated 2500 times per minute. using constant specific heats at room temperature, determine the thermal efficiency of this cycle and the rate of heat input if the cycle is to produce 90 kw of power.