How Many Significant Figures for Time and Mass Calculations?

[helpmedude]

Hi just a quick question about sig figs. If one was too divide a time such as 21.76s into increments of twenty to find the period of revolution for a centripetal force experiment would the answer be two or four significant figures? also if I multiply a mass such as 2567kg by acceleration due to gravity should my final answer be two significant figures? I am sure the answer to my second question is yes but the first I am not so sure about.

 

[mgb_phys]

21.76 is 4 sig figures. If you measured say 20 rotations to get this answer then yes, you know the time of one rotation to 4sig figures.

If you have a mass of 2567kg (again to 4 sig fig) and divide by g=9.81 then you only have 3sig figures in you answer. Or more correctly you have mass of 2567 +- 0.5kg and g=9.81 +- 0.005 so you know g to 1 part in 2000 you would know your answer to 1 part in 2000, ie approx +- 1kg.
If you used g=9.7 then you have only 2sig figures and an error of 1 part in 100.