To solve this problem, we will evaluate the net force acting on each object by analyzing the force vectors in the diagrams:

Observations:

1. Diagram (i): Two forces of equal magnitude $F$ act in opposite directions (horizontal line). The net force is zero since they cancel each other out.

   • $\text{Net Force} = F - F = 0$.

2. Diagram (ii): Two forces of equal magnitude $F$ act at an angle of 135° to each other. Their vector sum does not cancel out, resulting in a net force. (Requires vector addition for precise calculation, but it’s non-zero.)

3. Diagram (iii): Two forces of equal magnitude $F$ act at 90° to each other. The resultant force is not zero, as the magnitude can be calculated using Pythagoras:

   • $|\text{Net Force}| = \sqrt{F^2 + F^2} = \sqrt{2}F$.

4. Diagram (iv): One force $F$ acts to the left, and another force $2F$ acts to the right. The net force is non-zero, pointing to the right:

   • $\text{Net Force} = 2F - F = F$.

Answer:

The object with a net zero force acting on it is Diagram (i).

Let me know if you want further clarification or help with vector calculations.

Related Questions:

1. How do you calculate the net force when forces act at different angles?
2. What is the resultant vector magnitude for Diagram (ii)?
3. Why is the net force in Diagram (iii) proportional to $\sqrt{2}F$?
4. How does increasing the angle between vectors affect the net force?
5. Can we achieve zero net force with three vectors of different magnitudes?

Tip:

To calculate the net force in non-parallel cases, use vector addition by breaking forces into components along the x and y axes.