# What is the absolute uncertainty in your estimate of the total mass?

1. Sep 19, 2009

### simond

1. The problem statement, all variables and given/known data
You measure the mass of a physics textbook to be 2.97±0.07 kg, and use this value to estimate the total mass of 800 identical physics textbooks in the bookstore. What is the absolute uncertainty in your estimate of the total mass?

I have been working on this for a while. I am not sure why I cannot get it. What I have tried is:

0.07(2)=0.014 -- since the uncertainty can go up or down .07kg

then, multiplying the 0.014 by the 800 text books, to get 11.2kg.

This however apparently is incorrect. What should I do?

2. Sep 19, 2009

### Gear300

For a value x±dx, in which the error is ±dx, your absolute uncertainty is |±dx| = |dx|. So the magnitude of the maximum error you can get for a book is .07kg. So instead of the .14kg you used, it would be .07kg.

If what I said doesn't work, then it is probably because you're using 0.07(2) = 0.014...which is not right, its actually 0.14.