How many significant figures are in the measurement 0.020 km?

Two significant number are in the measurement 0.020 km

Explanation:

Given value is 0.020 km.

Significant figure :

Significant figures of a number are numbers that have significance to contribute to its resolution of measurements. This involves all numbers except the following: all leading zeros.

So, the significant number in this number is 2 and 0.

Hence, Two significant number are in the measurement 0.020 km

where are the vectors ?

no. dot product   =0 when vecs at right angles