Question

A racetrack measures 1.0000 x 10³ meters. A racecar completes a lap of this track in 20.4 seconds. To the proper number of significant figures, how should the average speed be reported?

	A.	49 meters/sec
	B.	49.0 meters/sec
	C.	49.020 meters/sec
	D.	49.02 meters/sec
	E.	50 meters/sec

Answer 1

Average speed = distance / time

= 1.0000 x 10³ / 20.4 m/s

= 49.0196 m/s

But, according to the rule when two numbers are divided or multiplied the answer must be reported in the LEAST NUMBER OF SIGNIFICANT FIGURES among the two numbers.

1.0000 x 10³   5 significant figures

20.4   3 significant figures

Therefore, 20.4 has the least significant figures and hence the answer must be reported in 3 significant figures.

ANSWER : 49.0 m/s (3 significant figures)

option B is correct.