A small metal bar whose initial temperature is 30° C is dropped into a container with boiling water, how long will it take to reach 80° C if it is known that it increases 3° in one second? How long will it take to reach 98°? solve by body cooling method.

"The body cooling (or warming) method you're referring to is likely based on Newton's Law of Cooling. However, the information given describes a scenario where the temperature of the metal bar increases at a constant rate of 3° C per second rather than following Newton's Law of Cooling, which states that the rate of heat loss of a body is directly proportional to the difference in the temperatures between the body and its surroundings.

If the temperature of the bar increases by 3° C each second, then we can calculate the time it takes to reach a certain temperature by simple arithmetic, assuming this rate of temperature increase remains constant. This isn't really using the body cooling method but rather a linear temperature increase model.

To reach 80° C from 30° C at a rate of 3° C per second, the increase needed is:
80° C - 30° C = 50° C

At a rate of 3° C per second, the time t required to increase 50° C is:
t = \frac{50° C}{3° C/second}

Similarly, to reach 98° C from 30° C:
98° C - 30° C = 68° C

The time t required to increase 68° C at the same rate is:
t = \frac{68° C}{3° C/second}

Let's calculate both.

To reach 80° C from 30° C, it will take approximately 16.67 seconds, and to reach 98° C, it will take approximately 22.67 seconds, given the constant rate of temperature increase of 3° C per second.

\boxed{16.67\text{ seconds}} and \boxed{22.67\text{ seconds}}