If steam enters a turbine at 600°k and is exhausted at 200°k, calculate the efficiency of the engine.

If in you machine you put some heat X, the machine will return some work W and some heat Y. In this case, X = 600k and Y = 200k.

The efficiency of a machine is the ratio of heat transformed into work, so

E = W/X = 1 - Y/X = 1 - 200/600 = 1 - 1/3 = 0.66.

So the efficiency of the turbine is of the 66%

luster is not a good characteristic to use by itself because luster is the property of minerals that indicates how much the surface of a mineral reflects light. the luster of a mineral is affected by the brilliance of the light used to observe the mineral surface.

there are no contact forces mentioned on the list of choices that you've provided.