For each of the following cases, indicate whether the work done on the second object in each example will have a positive or negative value. a. The road exerts a friction force on a speeding car skidding to a stop.
b. A rope exerts a force on a bucket as the bucket is raised up a well.
c. Air exerts a force on a parachute as the parachutist falls to Earth.

Air initially at 0.75 bar, 1000 k, and occupying a volume of 0.12 m^3 undergoes two processes. process 1-2: the air is compressed isothermally until the volume is halved. process 2-3: the air undergoes a constant pressure process until the volume is halved again. assume ideal gas behavior. a) determine the mass of the air, in kg. b) the work and the heat transfer for each of the two processes, in kj. (100 kj = 1 bar . m^3)