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UPSC Civil Service Exam Questions - Engineering

Q1:

If the diameter of a shaft subjected to torque alone, is doubled, then the horse power P can be increased to

A 16 P

B 8 P

C 4 P

D 2 P

ANS:B - 8 P

Shear stress = 16T/π*D^3.
So,
T IS PROPORTIONAL TO D^3.
POWER=2*pi*NT/60.

OVERALL.
POWER IS PROPORTIONAL TO T AND T IS PROPORTIONAL TO D^3.

So, POWER IS ALSO PROPORTIONAL TO D^3,
HERE.
D'=2D.
So,
P'=8P.