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#1
30092010
STPM Phycis [Help]
I'm very confused.
Suppose,question 1(a),i get the asnwer: x=1.3456 =1.35(correct to 3 sf) Then,for 1(b),it requires me to substitute the answer from 1(a),which should i choose?1.3456 or 1.35? I hope there is some reliable answer(preferable refer to previous STPM answer scheme).I cant get any confirmed(trusted) answer from my teacher(s) or friends from other school. 
The Iron Boot
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#2
01102010
Re: STPM Phycis [Help]
Quote:
The reason to use 1.3456 instead of 1.35 is that the final answer for 1(b) may be different if you use three significant figures for your calculation instead of four. It is never a mistake to use more decimal places in your calculations for a more accurate final answer. Using the rounded off figure for your future calculations can bring about errors that will only get worse if there are more calculations that follow. The error that originates from the rounding off will be carried forward to the next calculation, and if you round off the next answer and it is to be used in another set of calculations, that error will be even greater. Take for example, I have a big mass of 6000 kg acting on a square plate of 1.25 metres. (a) Calculate the force acting on the square plate and report the answer in 2 significant figures. (b) Calculate the axial stress experienced by the square plate and report the answer in 3 significant figures. The axial stress can be defined as the force acting on the square plate divided by the area of the square plate. (a) Force = 6000 kg x 9.81 m/s^2 = 58860 N (report as 59000 N or 59 kN) (b) Stress = Force / Area = 58860 N / (1.25 x 1.25) m^2 = 37670.4 Pa (report as 37700 Pa or 37.7 kPa) If you had used the answer in part (a), that is 59 kN, and substitute that in part (b), you would have got 37.8 kPa, and not 37.7 kPa. The difference here may seem small, but imagine that you will use the answer in part (b) for perhaps part (c) or part (d) in your exams. Also, some teachers might even mark you wrong for writing 37.8 kPa instead of 37.7 kPa. Therefore, play safe. The final answer counts, so it's better not to use rounded off figures for future calculations. In engineering practice, especially, it's considered bad practice to use rounded off figures for future calculations. Sometimes, the difference by onehundredth of a millimetre counts. Last edited by henry_yew; 01102010 at 01:50 AM. 

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Super Junior Member

#3
06102010
Re: STPM Phycis [Help]
Thx for your reply,appreciate it^^

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