Answer:
1) -275C
2) Less than or equal to -11C/min.
Step-by-step explanation:
Currently, the sample is 3C.
So, in order for our sample to freeze, it must <em>decrease </em>to -272C.
Part A)
So, to find how much the temperature must change, we can subtract the current temperature from the desired temperature.
So:
Therefore, the temperature must change by -275C.
The negative tells us that the temperature must <em>decrease</em> by <em>at least</em> 275C in order to ensure that the helium freezes.
Part B)
Let <em>t</em> represent the temperature change per minute.
We know that the change must be -275C or greater.
Therefore, we can write the following inequality:
.
We can divide both sides by 25. So:
Therefore, it tells us that in order for the helium sample to freeze in 25 minutes, the change in temperature per minute must be less than or equal to -11C.