1) A block of mass m is held stationary on a ramp by the frictional force on it from the ramp. A force F, directed up the ramp, is then applied to the block and gradually increased in magnitude from zero. Sketch the friction force as a function of time. Hint: be careful about the signs! 2) A

An air standard cycle with variable specific heats is executed in a closed system and is composed of the following four processes. 1-2 isentropic compression 100 kpa and 22°c to 600 kpa 2-3 v=constant heat addition to 1500 k 3-4 isentropic expansion to 100 kpa 4-1 p=constant heat rejection to initial state (a) show the cycle on p-v and t-s s (b) calculate the net work output per unit mass (409 kj/kg) (c) determine the thermal efficiency (47.9%)