In a shaft, the shear stress is not directly proportional to A. Radius of the shaft B. Angle of twist C. Length of the shaft D. Modulus of rigidity

The correct answer is: C. Length of the shaft.

Shear stress is the force per unit area that acts parallel to a surface. It is caused by a shearing force, which is a force that tends to cause two parts of a material to slide past each other.

The shear stress in a shaft is proportional to the radius of the shaft, the angle of twist, and the modulus of rigidity. The modulus of rigidity is a measure of the stiffness of a material. It is the ratio of shear stress to shear strain.

The length of the shaft does not affect the shear stress. This is because the shear stress is caused by the shearing force, which is a force that acts perpendicular to the length of the shaft.

Here is a more detailed explanation of each option:

• A. Radius of the shaft: The shear stress is proportional to the radius of the shaft because the larger the radius, the more material there is to resist the shearing force.
• B. Angle of twist: The shear stress is proportional to the angle of twist because the larger the angle of twist, the more the material is being deformed.
• C. Length of the shaft: The shear stress is not proportional to the length of the shaft because the length of the shaft does not affect the shearing force.
• D. Modulus of rigidity: The shear stress is proportional to the modulus of rigidity because the higher the modulus of rigidity, the stiffer the material and the more it can resist the shearing force.