Question

the net electric force acting on each of the three objects below is sketched as a green arrow. for example, if the green arrow points to the left the object feels a net electric force pushing it to the left. if there is no green arrow, the object feels no net electric force.
use this information to assign an electric charge to each object. that is, decide whether each object has a positive electric charge, a negative electric charge, or is neutral.
note for advanced students: there may be more than one correct answer.

Explanation:

To solve this, we analyze the electric force direction (green arrows) and use the rules of electric charges (like charges repel, opposite attract):

Top Object (Upward Arrow)

The net force is upward. For a charge to have an upward net force, we consider the forces from other charges. If the middle object (and bottom, depending on setup) influences it, a positive charge might experience a repulsive force upward (if another positive is below, repelling) or an attractive force upward (if a negative is below, attracting). Alternatively, if the force is due to an electric field, the direction of force on a positive charge is in the direction of the electric field. Assuming the arrow direction is the net force, a positive charge’s force direction matches the electric field (or net force from other charges) direction. So we assign + (positive) here.

Middle Object (No Arrow)

No green arrow means no net electric force. This implies the net force from other charges (top and bottom) is zero. A neutral charge (0) has no net force (since it doesn’t interact with electric forces from charges, or if charges above and below cancel out). So we assign 0 (neutral) here.

Bottom Object (Downward Arrow)

The net force is downward. Similar to the top, a negative charge might experience a downward force: if a positive is above (attracting downward) or another negative below (repelling downward). The force direction on a negative charge is opposite to the electric field, so a downward force on a negative charge would mean the electric field (or net force from other charges) is upward. So we assign - (negative) here.

Final Assignments:

• Top: \( + \)
• Middle: \( 0 \)
• Bottom: \( - \)

(Note: The exact assignment depends on the implicit charge configuration, but this follows the “no net force = neutral, force direction matching charge sign logic”.)

Answer:

Top: \( \boldsymbol{+} \), Middle: \( \boldsymbol{0} \), Bottom: \( \boldsymbol{-} \)