College Physics Problem 1.20

(a) A person’s blood pressure is measured to be 120±2 mmHg. What is its percent uncertainty?

(b) Assuming the same percent uncertainty, what is the uncertainty in a blood pressure measurement of 80 mmHg?


Part a

The percent uncertainty is computed as

\displaystyle \%\:uncertainty=\frac{2\:mmHg}{120\:mmHg}\times 100\%=1.7\%

Part b

The uncertainty in the blood pressure is

\displaystyle \delta _{bp}=\frac{1.7\:\%}{100\:\%}\times 80\:mmHg=1.3\:mmHg