When an object is placed 8 millimeters from a concave spherical mirror, a clear image can be projected on a screen 16 millimeters in front of the mirror. if the object has a height of 4 millimeters, the height of the image is
a. 2 millimeters.
b. 4 millimeters.
c. 8 millimeters.
d. 12 millimeters.

Air is contained in a variable-load piston-cylinder device equipped with a paddle wheel. initially, air is at 400 kpa and 17°c. the paddle wheel is now turned by an external electric motor until 75 kj/kg of work has been transferred to air. during this process, heat is transferred to maintain a constant air temperature while allowing the gas volume to triple. calculate the required amount of heat transfer in kj/kg.