A cart rolls 12.0 m in 5.3 s. A calculator says the speed is 2.2641509 m/s. Did anyone really measure that speed to eight figures?
In earlier grades you saw speed = distance ÷ time. You've already seen how to count a measurement's significant figures.
A calculator hands back as many digits as fit on its screen. The measurements never justified most of them. A calculated result can never be more precise than the measurements that produced it.
In the cart example, 12.0 m has three significant figures and 5.3 s has two, so the time is the limiting value. 12.0 ÷ 5.3 = 2.2641509… Round to two significant figures: the speed is 2.3 m/s.
In this course, round this way whenever you multiply or divide measured values.
A toy drone flies 7.25 m in 2.0 s. Report its speed to the correct number of significant figures.
Divide:
7.25 ÷ 2.0 = 3.625
Count the significant figures: 7.25 m has three; 2.0 s has two. Two is the fewest.
Round to two significant figures:
speed = 3.6 m/s
A ball rolls 9.0 m in 4.1 s. Calculate its speed in m/s and report it to the correct number of significant figures.
A walker covers 8.44 m in 2.0 s. Calculate the speed in m/s and report it to the correct number of significant figures.
A conveyor belt moves at a steady 2.5 m/s for 3.14 s. Calculate the distance covered in meters and report it to the correct number of significant figures.
A cart travels 15.5 m in 4.00 s. Calculate its speed in m/s and report it to the correct number of significant figures.
A marble rolls 0.60 m in 0.244 s. Calculate its speed in m/s and report it to the correct number of significant figures.
A remote-controlled car drives 4.4 m in 1.1 s. Calculate its speed in m/s and report it to the correct number of significant figures.