What is the approximate weight of a 20.kg rock

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Discussion Overview

The discussion revolves around the interpretation of the notation "20.kg" in relation to significant figures and the calculation of weight using the formula for weight (mass times gravitational acceleration). Participants explore the implications of different representations of mass on the accuracy of the resulting weight calculation.

Discussion Character

  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant calculates the weight of a 20.kg rock as 196N, suggesting rounding to 200N based on significant figures.
  • Another participant questions the meaning of "20.kg," expressing confusion over its notation compared to "20 kg" and "20.0 kg."
  • A participant clarifies that "20.kg" indicates that the zero is significant, contrasting it with "20 kg" which has only one significant figure.
  • There is a discussion about how scientific notation can clarify the significance of zeros in measurements, with an example provided as 2.0 x 10^1 kg.
  • One participant expresses frustration with their teacher's handling of significant figures, indicating a lack of confidence in the teacher's professionalism.

Areas of Agreement / Disagreement

Participants express differing views on the notation "20.kg," with some agreeing on its significance while others remain confused. The discussion does not reach a consensus on the interpretation of this notation.

Contextual Notes

There is uncertainty regarding the standard interpretation of the notation "20.kg," and participants rely on their understanding of significant figures without resolving the ambiguity of the notation itself.

vaironl
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Since it has a decimal it would be 20kg * 9.8m/s which equals 196kg m/s^2 = 196N

But the decimal means i have to round two sig figs, which would make it 200N?

A very simple problem, I really don't know why I'm asking it.
 
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tiny-tim said:
hi vaironl! :smile:

do you mean 20.0 kg ?

if so, that's three significant figures :wink:

Thanks for the reply, tim. "And let me say, that is a big post count"

My paper says 20.kg so I'm rounding to two significant figures. Am I right?
 
i've no idea what "20.kg" means :redface:

i understand "20 kg" and "20.0 kg", but I've never seen "20.kg" or even "20. kg" :confused:
 
Yes that is correct. When you see things like 20.kg, it means that the 0 is significant. If it were simply 20kg without the decimal, that would mean the number is only accurate to 1 significant figure. If, as tiny-tim advised, it were 20.0 kg, it would mean the second 0 is significant as well and there are 3 significant figures to take into account.

So your answer is 200N, accurate to 2 significant figures.

Scientific notation is really great because it clears these kind of odd notations. 20kg to 2 significant figures in SI notation would be 2.0 x 10^1 kg, clearly showing the 0 is significant.
 
ah! thanks, Pengwuino! :smile:
 
tiny-tim said:
i've no idea what "20.kg" means :redface:

i understand "20 kg" and "20.0 kg", but I've never seen "20.kg" or even "20. kg" :confused:

Pengwuino said:
Yes that is correct. When you see things like 20.kg, it means that the 0 is significant. If it were simply 20kg without the decimal, that would mean the number is only accurate to 1 significant figure. If, as tiny-tim advised, it were 20.0 kg, it would mean the second 0 is significant as well and there are 3 significant figures to take into account.

So your answer is 200N, accurate to 2 significant figures.

Scientific notation is really great because it clears these kind of odd notations. 20kg to 2 significant figures in SI notation would be 2.0 x 10^1 kg, clearly showing the 0 is significant.

Thanks, I knew something was going wrong. My teacher usually does things like that.
I can't believe sometimes he even gets about 3-6 problems incorrectly which demonstrates unprofessional work ethic.
 

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