Final answer:
The statement is true. Shear deformation occurs when two antiparallel forces of equal magnitude are applied to opposite surfaces of a solid object, causing equal-magnitude shear stresses on three other planes.
Step-by-step explanation:
The statement that if a shear stress acts on one plane in an object, then equal-magnitude shear stresses act on three other planes is true.
Shear deformation occurs when two antiparallel forces of equal magnitude are applied tangentially to opposite surfaces of a solid object, causing no deformation in the transverse direction to the line of force. This results in a gradual shift of layers in the direction tangent to the acting forces.
For example, two antiparallel forces are applied to opposite parallel surfaces of the object. This causes a shear deformation characterized by a shift of layers, resulting in equal-magnitude shear stresses on three other planes.