15) Principal planes in a strained body are

Answer is:

Planes which have no shear stress

Explanation:

Principal Stresses and Strains: It has been observed that at any point in a strained material, there are three planes, mutually perpendicular to each other, which carry direct stresses only, and no shear stresses.

A little consideration will show that out of these three direct stresses, one will be maximum, the other minimum and the third an intermediate between the two. These particular planes, which have no shear stress, are known as principal planes. The magnitude of direct stress, across a principal plane, is known as principal stress.

ISRO Technical Assistant Mechanical Question Paper - 2017 with Answer Key

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16) A 5 m long ladder is resting on a smooth vertical wall with its lower end 3m from the wall. What should be the coefficient of friction between the ladder and the floor for equilibrium?

Answer is:

(3/8)

17) Newton's law of viscosity states that for a Newtonian fluid, the

Answer is:

Shear stress is proportional to rate of shear strain

Explanation:

According to Newton’s law of viscosity, the shear stress on a layer of a fluid is directly proportional to the rate of shear strain. Ideal fluid is a fluid with zero viscosity. Real fluids possess viscosity.