Final answer:
Newton's Law of Cooling is used to calculate the cooling rate of coffee.
Step-by-step explanation:
The situation described in your question pertains to Newton's Law of Cooling. This law states that the rate of change of temperature of an object is proportional to the difference between its own temperature and the ambient temperature (i.e. the temperature of its surroundings). In this case, the coffee is cooling in a room whose temperature is 25° C.
According to this law, we have the relationship: (change in temperature) / (time taken) = k * (temperature difference between the system and the surroundings), where 'k' is a constant coefficient.
In this case, the change in temperature is (90-50)° C = 40° C, and the time taken is 20 minutes. We can use this information to find the value of 'k', this is: k = (change in temperature) / (time taken * temperature difference). After finding the value of 'k' you can plug in the numbers and solve to get your answer, however, note that this is an estimation, as Newton's law of cooling is an oversimplification of the real-life processes involved in cooling.
Learn more about Newton's Law of Cooling