# Homework Help: Equations of motion and proper Significant Digits.

1. Sep 24, 2007

### JamesJames

1. The problem statement, all variables and given/known data

Solve the following to the proper number of significant figures:

a) A loaded truck has mass (2.12 X 10^4 +/- 6 X 10^2) kg and when empty, it has a mass of (1.72 X 10^4 +/- 5 X 10^2) kg. What is the relative uncertainty of the mass of the gravel dumped from the truck?

3. The attempt at a solution

Ok, so I go through the math and get

Relative Uncertainty = (5 X 10^2 + 6 X 10^2) kg / 4000 = 0.275

My qwuestion is in regards to significant digits. According to me, the # of sig. figs. Here is 1……there is 1 sig. fig. in 5 X 10^2 or 6 X 10^2, whichever you look at, so the answer should be rounded off to one significant figure.

This means that the FINAL answer should be 0.3.

b) v(initial) = 10.5 m/s
v(final) = -7.3 m/s
t = 0.0115 s

Calculate a.

3. The attempt at a solution

I used v(final ) = v(initial) + at and got a = 1533 m/s^2.

Should the correct answer (rounded off to proper number of significant figures) be a = 1.53 X 10^3 m/s^2?

What about 1533 m/s^2 or 1530 m/s^2….would either of these be acceptable OR is the only answer 1.53 X 10^3 m/s^2?

2. Sep 25, 2007

### JamesJames

Your help would be greatly appreciated. I feel like I am close but just need some help finishing off the problems.

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