# Torsion problem finding d!

1. Dec 1, 2009

### markles

Hello I recently got handed this problem and I had a fair idea on how to go about it or so I thought! My only problem is I do not know how to find d? I would be grateful if someone could show me how to find d and show me the equation used

Thank you

1. The problem statement, all variables and given/known data

A steel shaft 3m long is transmitting 1MW at 240rev/min. The working conditions to
be satisfied by the shaft are:

(a) that the shaft must not twist more than 0.02radian on a length of 10 diameters;

(b) that the working stress must not exceed 60MN/m2.

If the modulus of rigidity of the steel 80GN/m2 what is

(i). the diameter of the shaft required;

(ii). the actual working stress;

(iii). the angle of twist of the 3m length?

2. Relevant equations

T/J=Gxtheta/L=t/R
T=power/W

3. The attempt at a solution

(1x106) /(240/2pi/60)= T = 39.793KN

J= pi x d4/32
diameter=d
T= Torque
G =mod of rigidity
J= polar second moment of area???

d=?????

G=80x109

G x theta (0.02) = 1.6x109/10d

what is the diameter??? and how would i go about finding it???

thanks

Last edited: Dec 1, 2009