If your speedometer has an uncertainty of 2.0 km/h at a speed of 90 km/h, what i
ID: 1654044 • Letter: I
Question
If your speedometer has an uncertainty of 2.0 km/h at a speed of 90 km/h, what is the percent uncertainty? (b) If it has the same percent uncertainty when it reads 60 km/h, what is the range of speeds you could be going? A person's blood pressure is measured to be 120 plusminus 2 mm Hg What is its percent uncertainty? (b) Assuming the same percent uncertainty, what is the uncertainty in a blood pressure measurement of 80 mm Hg? A person measures his or her heart rate by counting the number of beats in 30 s If 40 plusminus 1 beats are counted in 30.0 plusminus 0.5 s what is the heart rate and its uncertainty in beats per minute?Explanation / Answer
19. (a) % uncertainty = (2 / 90) x 100
= 2.2 %
(b) Uncertainty = 60 x 2.2 / 100 = 1.3 km/h
so speed range = 60 - 1.3 to 60 +1.3
= 58.7 km/h to 61.3 km/h
20. (a) % = (2 / 120) x 100 = 1.7%
(b) uncertainty = 80 x 1.7 / 100
= 1.3 mm Hg
21. heart rate = (40)/30 = 1.33 beats per sec
uncertainty = 1.33 sqrt[ (1 /40)^2 + (0.5/30)^2]
= 0.04
heart rate = 1.33 +- 0.04 beats /s
per min = 80.0 +- 2.4