Can anybody help me ive been stuck for over 3 weeks

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A solid steel shaft of 10 m length and 70 mm diameter is subjected to a torque of 4.5 kNm, and the goal is to replace it with a thin-walled hollow shaft of 10 mm wall thickness while maintaining the same torque capacity and maximum allowable stress. The discussion highlights the need to derive the stress equation in terms of radius to find the required diameter of the hollow shaft. Participants emphasize that the problem is a standard homework question, suggesting that understanding the relevant equations and showing work is crucial for solving it. There is also a request for hints or explanations rather than complete solutions, indicating a desire for guidance in grasping the concepts involved. The conversation underscores the importance of applying theoretical knowledge to practical engineering problems.
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A solid steel shaft 10 m long and 70mm diameter is subjected to a torque of 4.5 kNm.
In order to save the weight the solid shaft is to be replaced be a thin walled hollow shaft of wall thickness 10mm.
What diameter of hollow shaft is required to carry the same torque if the maximum allowable stress is the same as that experienced by the solid shaft?
If the modulus of rigdity of the steel is 80 x 109 N/m2 calculate the angle of twist for the thin walled shaft.
Considering materials/ manufacturing costs and application constraints such as weight, inertia, balance, size and reliability, describe a suitable application for each type of shaft stating why that type is more suitable than the alternative.
Ive spent 3 weeks on this darn question
 
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What part of the question are you stuck on? This seems like a 20 min. homework problem.

You can write the stress equation completely in terms of radius (given the additional information you have). From there, simply solve for it.
 
TWOSWORDALI: This sounds like a take-home final exam question, and is one of the questions on the test you posted two weeks ago in thread [thread=324821]324821[/thread]. The PF rules state we are not allowed to tell you how to approach or solve your homework problem. You must list relevant equations yourself, and show your work; and then someone might check your math.
 
no this is not a take home exam at all its a question for homework for the HNC. And I am completely LOST As far as the electrical goes I am doing alright but this is one question out of 10 that I am stuck on well its another one as well dealing with shear force an d the bending moment diagram. But this question has got me crazy. No it is not a takehome exam in the attached file is the questions that I am doing. A hint or someexplanation or somthing will be very helpful, no i do not want you to do it for me but i do seriously need some help in understanding this. Imcompletely dumbfounded with it you can check Manchester open learning and show them the question they will affirm that it is not a take home exam question
 
If two beams can both carry the same torque, then its reasonable to say that they can be stressed the same amount. Having said that.

What is the equation for torsional stress?
 

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