Question

suppose two children push horizontally, but in exactly opposite directions, on a wagon containing a third child. the first child exerts a force of $f_1 = 75.0 n$, the second a force of $f_2 = 95.0 n$, friction is $12.0 n$, and the mass of the third child plus wagon is $22.0 kg$. (a) what is the system of interest if the acceleration of the child in the wagon is to be calculated? (select all that apply.) the child in the wagon the wagon the children outside the wagon (b) which of the following diagrams correctly represents the free - body diagram for the situation described here?

Explanation:

(a) When calculating the acceleration of the child in the wagon, the system of interest is the child - wagon combination as a whole. The children outside the wagon are external agents applying forces on the system.
(b) In a free - body diagram for the child - wagon system, the normal force ($\vec{N}$) acts upwards, the weight ($\vec{W}$) acts downwards, the two applied forces $\vec{F}_1$ and $\vec{F}_2$ act horizontally in opposite directions and the frictional force $\vec{f}$ acts horizontally opposite to the net applied force. The correct orientation has the normal force upwards and weight downwards, so the first diagram is correct.

Answer:

(a) the child in the wagon, the wagon
(b) the first diagram (with $\vec{N}$ upwards and $\vec{W}$ downwards)