Question

Two shafts A and B are made of the same material. The diameter of shaft B is thrice that of shaft A. What is the ratio of power which can be transmitted by A to power that can be transmitted by shaft B?

• A. 1/81
• B. 1/3
• C. 1/9
• D. 1/27

Answer 1

Answer:

D. 1/27

The power transmitting capacity of a shaft is given by $P =\frac {2\pi NT}{60}$ The ratio of power transmitted by shaft A to shaft B is $(D_{A} / D_{B}) ^ 3$As the power is proportional to the diameter cubed, the power transmitting capacity is proportional to the diameter cubed. Given $D_{B} = 3D_{A}$ the ratio of power transmitted by A to B is $1/27$