TrueTears question thread

[TrueTears]

A 50V DC voltage is applied across the terminal P-Q what is the voltage across the terminals X-Y?

Thanks

[arthurk]

30V? seeing as the 1000 ohm resistor is in parallel thus is negligible when determinging voltage out
2000 and 3000 ohms in series then calculate the voltage out across the 3000 ohm resistor
not sure if thats right though

[TrueTears]

30V? seeing as the 1000 ohm resistor is in parallel thus is negligible when determinging voltage out
2000 and 3000 ohms in series then calculate the voltage out across the 3000 ohm resistor
not sure if thats right though

yeap thanks just got it.

[naved_s9994]

30 V...that exact Q, or something similar was on STav 09

[dejan91]

Yeah that was the one on STAV 09.

[Damo17]

It is easy to see that it is . so the voltage drop across the resistor will be and the combined voltage drops across the and resistors will also be . The resistor takes of the voltage drop across, therefore voltage across the resistor/XY will be

[TrueTears]

Thanks. ^^^

Also this one:
The yield strength of mild steel is Pa. what is the minimum diameter of mild steel rod that can support a 75kg man with a safety factor of 3 before breaking?

What does it mean by safety factor? Because sometimes in the questions I've done in the past, I divide the stress with the safety factor and sometimes multiply the force applied with the safety factor. What is the actual systematic way of understanding "safety factor"?

[kurrymuncher]

If you are given the max stress of an object and a safety factor of 3. You then divide that max stress by 3, and that is the new stress of the object. You then use this new stress value with the weight of the 75kg man, to find the area etc etc.

the safety factor is used to pretty much ensure that the object does not reach its maximum stress and then fail, they take a safety factor so that can safely apply a force without any danger of failing.

this of the top of my head, hopefully sum1 can confirm

[Damo17]

Thanks. ^^^

Also this one:
The yield strength of mild steel is . what is the minimum diameter of mild steel rod that can support a 75kg man with a safety factor of 3 before breaking?

What does it mean by safety factor? Because sometimes in the questions I've done in the past, I multiply the stress with the safety factor and sometimes the force applied. What is the actual systematic way of understanding "safety factor"?

I'm not doing structures but I'll try and help as much as possible. Safety factors, usually from 4 to 10, are a way of accounting for any unknown weaknesses in the materials actually being used. For example, if a steel cable is capable of supporting a load of 500 kg, the manufacturer might consider a safety factor of 5 is appropriate, and so recommend that it be used for masses no greater than 100 kg.

So for your question:
so max weight the steel can hold is 75kg* 3=225kg
Then the max force it can handle is 225 *10=2250N

You are trying to find the diameter but first you need the Area.



    



  

[Damo17]

If you are given the max stress of an object and a safety factor of 3. You then divide that max stress by 3, and that is the new stress of the object. You then use this new stress value with the weight of the 75kg man, to find the area etc etc.

Wants it before breaking therefore you use the max stress.

[kurrymuncher]

lol Im not sure, wait for mao

[TrueTears]

Thanks guys!!! I got it

Safety factor:

A multiplier applied to the calculated maximum force or a number that the tensile strength is divided by in order to determine the safe working load.

Both will give same answer

[Damo17]

Yeah you can do it both ways. Stupid me.  :crazy2:

[methodsboy]

i think there's another one:
Recommended max stress (given in question) = stress(use this for other calculations) / safety factor
ONLY USE when it states the "recommended max stress"

[methodsboy]

Thanks guys!!! I got it

Safety factor:

A multiplier applied to the calculated maximum force or a number that the tensile strength is divided by in order to determine the safe working load.

Both will give same answer

where safe working load = allowable stress =]