In a single subject research, a group of observations at the same individual under the same conditions is a(

Phase

Explanation:

A phase of a single subject research has a single set of environmental factors. These factors are constant in one phase.

The environmental factor is considered the independent variable which is plotted in the x axis.

The response of the subject is considered the dependent variable which is plotted in the y axis. This gives us the relation of the dependent and independent variable of the subject.

b.a device that inputs heat into a cool object

f=ma newton

f=100x2.5=250n