Heat engine uses thermal energy flowing from a heat source that is 225 k to a cold sink that is 50 k. what is the approximate efficiency of the heat engine?

77.8 %

Explanation:

The efficiency of a heat engine is given by:

where is the temperature of the cold sink and is the temperature of the heat source. In this problem,

so the efficiency is

air exerts forces on falling objects near earth’s surface.

explanation:

the term 'free falls' refer to object that are falling towards the earth, in a situation in which gravity is the only force acting on the object.

for an object in free fall, the acceleration is constant (g, the gravitational acceleration), and so the velocity of the object constantly increases.

for objects near earth's surface, there is always another force acting on the object: the resistance due to the air. this force is opposed to the direction of fall of the object, and it is proportional to the velocity of the object, so as the object falls down, this force increases up to a point when it balances the force of gravity, and the object continues its motion at constant velocity (called terminal velocity). since in this case gravity is not the only force acting on the object, we are not in a situation of free fall.