(a) what is the system of interest if the acceleration of the child in the wagon is to be calculated? (select all that apply.)

since child is moving along with the wagon and we need to find the acceleration of child inside that wagon then in this case the system of interest must be child + wagon

System of interest will be the system that is used to find the force or acceleration using Newton's law

Here we have to assume that system on which if we will calculate the forces then the net value of force on that system will help to calculate the unknown quantities

So here our system will be boy + wagon

i don't understand. explain it clearly

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