Physics/Engineering question
Discussion
OP
Stop mixing up your units!
Force = N
Stress = N/m2
Length = M
Area = M2
etc
and three significant figures is fine for the vast majority of equations, in the real world you'll feel quite pleased to predict anything to within 5% so anything past the third significant figure is going to be 0.1% which won't matter.
Mixing units is bad practice but it happens. I have worked with metric analysis that was used to give numbers to an imperial project so ended up with graphs of psi stress versus N load, but in general just avoid doing anything like this.
Stop mixing up your units!
Force = N
Stress = N/m2
Length = M
Area = M2
etc
and three significant figures is fine for the vast majority of equations, in the real world you'll feel quite pleased to predict anything to within 5% so anything past the third significant figure is going to be 0.1% which won't matter.
Mixing units is bad practice but it happens. I have worked with metric analysis that was used to give numbers to an imperial project so ended up with graphs of psi stress versus N load, but in general just avoid doing anything like this.
Harding91 said:
Assignment is due in next week just finished writing up the final draft.
In regards to this whole thread, this is how i've put the answer to the question.
The question :
When the lift is close to the bottom of the lift shaft, the cable has a length of 95 m. Show that the mass of the lift fully loaded as described in (d) above, stretches the cable by about 15 mm.
(4 marks)
I will again update this when i get it back marked, should be by the end of the month.
Again i appreciate everyones comments and input but im still glad i stuck with what i got to myself and if im wrong im happy to be wrong and learn from it!
Sorry for coming across a bit strong OP, but you really should read the comments people have said in this thread.In regards to this whole thread, this is how i've put the answer to the question.
The question :
When the lift is close to the bottom of the lift shaft, the cable has a length of 95 m. Show that the mass of the lift fully loaded as described in (d) above, stretches the cable by about 15 mm.
(4 marks)
I will again update this when i get it back marked, should be by the end of the month.
Again i appreciate everyones comments and input but im still glad i stuck with what i got to myself and if im wrong im happy to be wrong and learn from it!
The cross sectional area of the cable is NOT 0.45 m^2
The change in length is NOT given, so you can"t use this to calculate E and then use that value to get back to the change in length.
And if I were marking this then you would lose marks for giving stupidly long non significant digits.
As you say, you're happy to go with what you did yourself and are happy to be wrong, which is ok. But why post in the first place?
ETA: it's not a problem mixing units for length in mm and area in m^2 here as strain is a dimensionless quantity, but you should give units of the values you calculate (E) - notwithstanding you can't calculate it given the information you have given. When giving units it is convention to leave a (thin) space between the quantity and the unit, and when writing quantities have a thin space between groups of 3 (thousands) for values (although numbers < 10 000 can be written as 1234).
Edited by V8LM on Friday 8th April 01:18
V8LM said:
Sorry for coming across a bit strong OP, but you really should read the comments people have said in this thread.
The cross sectional area of the cable is NOT 0.45 m^2
The change in length is NOT given, so you can"t use this to calculate E and then use that value to get back to the change in length.
And if I were marking this then you would lose marks for giving stupidly long non significant digits.
As you say, you're happy to go with what you did yourself and are happy to be wrong, which is ok. But why post in the first place?
ETA: it's not a problem mixing units for length in mm and area in m^2 here as strain is a dimensionless quantity, but you should give units of the values you calculate (E) - notwithstanding you can't calculate it given the information you have given. When giving units it is convention to leave a (thin) space between the quantity and the unit, and when writing quantities have a thin space between groups of 3 (thousands) for values (although numbers < 10 000 can be written as 1234).
I'd also add that there is really no need to go to such high significant figures, you won't get any more marks, and it gets messy with too many.The cross sectional area of the cable is NOT 0.45 m^2
The change in length is NOT given, so you can"t use this to calculate E and then use that value to get back to the change in length.
And if I were marking this then you would lose marks for giving stupidly long non significant digits.
As you say, you're happy to go with what you did yourself and are happy to be wrong, which is ok. But why post in the first place?
ETA: it's not a problem mixing units for length in mm and area in m^2 here as strain is a dimensionless quantity, but you should give units of the values you calculate (E) - notwithstanding you can't calculate it given the information you have given. When giving units it is convention to leave a (thin) space between the quantity and the unit, and when writing quantities have a thin space between groups of 3 (thousands) for values (although numbers < 10 000 can be written as 1234).
Edited by V8LM on Friday 8th April 01:18
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