A uniform bar of square cross-section is lying along a frictionless horizontal surface. A horizontal force is applied to pull it from one of its ends then

Correct Option: The bar is not under any stress because force has been applied only at one end

Step-by-Step Explanation:

1. Understanding Stress: Stress is defined as the internal restoring force per unit cross-sectional area that arises within a body when it is subjected to deforming external forces. For internal stress to develop, there must generally be opposing forces acting on the body that attempt to deform (stretch, compress, or shear) it.

2. Analyzing the Scenario: We have a uniform bar lying on a frictionless horizontal surface. A horizontal pulling force is applied at one of its ends. Since the surface is frictionless, there is no frictional drag or opposing force acting on the bar from the ground. Furthermore, no external opposing force is applied at the other end of the bar.

3. Motion of the Bar: Since there is no opposing force to resist the motion, the applied force causes the entire bar to accelerate freely as a single unit. The acceleration of the bar can be represented by:

$a=\frac{F}{m}$

where:
- $F$ is the applied horizontal force,
- $m$ is the mass of the bar.

4. Conclusion: Because the force is applied only at one end with no resisting force at the other end to cause deformation or elongation, the bar moves freely without any internal tension or deformation. Consequently, no internal restoring forces are developed, and the bar is not under any stress.