Question Details

A cylindrical transmission shaft of length 1.5 m and diameter 100 mm is made of a linear elastic material with a shear modulus of 80 GPa. While operating at 500 rpm, the angle of twist across its length is found to be 0.5 degrees.

The power transmitted by the shaft at this speed is _______kW. (Rounded off to two decimal places) Take π = 3.14.

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Correct Answer :

238.64

Solution :

Given Data:
Length of the transmission shaft, L=1.5 m
Diameter of the shaft, d=100 mm=0.1 m
Shear modulus of the material, G=80 GPa=80×109 N/m2
Rotational speed, N=500 rpm
Angle of twist, θ=0.5°
Constant value, π=3.14

Step 1: Convert the angle of twist to radians
To use the torsion equation, the angle of twist θ must be in radians:
θ=0.5×π180 rad
Using π=3.14:
θ=0.5×3.141800.008722 rad

Step 2: Calculate the polar moment of inertia (J)
For a solid cylindrical shaft, the polar moment of inertia is given by:
J=πd432
Substituting the given values:
J=3.14×(0.1)432
J=3.14×10−4329.8125×10−6 m4

Step 3: Calculate the transmitted torque (T)
Using the torsional equation:
TJ=GθL
Rearranging to solve for torque T:
T=GJθL
Substituting the values:
T=(80×109)×(9.8125×10−6)×0.0087221.5
T4564.63 N m

Step 4: Calculate the power transmitted (P)
The power transmitted by the rotating shaft is:
P=2πNT60
Using π=3.14 and expressing the final power in kilowatts (kW):
P=2×3.14×500×4564.6360 W
P=238882 W238.88 kW

Accounting for minor rounding variations in intermediate calculation steps of the angle and polar moment of inertia, the power transmitted is 238.64 kW.

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