Question

A balance measures mass to 0.001 g. If you determine the mass of an object that weighs about 30 g, would you record the mass as 30 g, 32 g, 32.1 g, or 32.075 g? Explain your choice by writ­ing one or two complete sentences that describe your thinking.

Answer 1

30g

Step-by-step explanation:

The true mass of the recorded will be 30g ±0.001g. This figure means that the actual mass recorded lies somewhere between either 29.999g or 30.001g. Both figures could be rounded to two significant figures giving 30g.

Hence the answer written is correct to two significant figures considering the uncertainty in the measurement of the mass.

Answer 2

The mass is recorded as 32.075 g

Step-by-step explanation:

"The first digit of uncertainty is taken as the last significant digit", this is the rule for significant figures in the analysis. The balance measures the mass up to three decimal places, so it makes the most sense to note the whole figure.