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Chapter: Mechanical : Strength of Materials : Torsion

Important Answers: Torsion

Mechanical - Strength of Materials - Torsion




1.     What are the assumptions made in torsion equation?

The material   of   the   shaft   is   homogeneous,   per

Twist is uniform along the length of the shaft and

The stress does not exceed the limit of proportionality


2. Write down the expression for power transmitted by a shaft.

Power, P = 2пNT/ 60    


T –Torque in kN.m       

N –Speed in r.p.m.        

P –Power in Kw   


3. Define polar modulus.       

It is the ratio between polar moment of inertia and radius of the shaft.


4. State the differences between closed and open coil helical springs.

Closed coiled helical springs


Adjacent coils are very close to each other

It can carry only tensile loads .

Helix angle is negligible


Open coiled helical springs


Large gap between adjacent coils

It can carry Both tensile and Compression loads.

Helix angle is considerable


5.Find the torque which a shaft of 50mm diameter can transmit safely, if the allowable shear stress in 75 N/mm²?

T = п/ 16 x fsx d3                                      

T = п/ 16 x 75 x (50)3                                         

T = 1.840 kN.m                                         


6. What is mean by stiffness?

The stiffness of the spring is defined as the load required to product unit deflection.


7.Classify the types of springs.

Torsion spring and

Bending spring


8.What is meant by spring?

Spring is a device which is used to absorb energy by taking very large change in its form without permanent deformation and then release the same when it is required.            


9.Define torsion.

When a pair of forces of equal magnitude but opposite in direction acting on body, it tends to twist the body. It is known as twisting moment or simply as torque.             


10.what is meant by torsion spring?

A spring, which is subjected to torsion or twisting moment only is known as torsion spring.



11. What is the ratio of maximum shear stress to the average shear stress in the case of solid circular section?


Qmax is 4/3 times the Qavg.


12. What is the shear stress distribution value of Flange portion of the I-section?



Where, D- depth


y- Distance from neutral axis


13. Where the shear stress is max for Triangular section?


In the case of triangular section, the shear stress is not max at N A. The shear stress is max at a height of h/2


14. Define: Mohr’sTheorem for slope


The change of slope between two points of a loaded beam is equal to the area of BMD between two points divided by EI.



15. Define: Mohr’sTheorem for deflection


The deflection of a point with respect to tangent at second point is equal to the first moment of area of BMD between two points about the first point divided by EI.


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