What does it mean axis 1-1' ?

axis=0 (or axis='rows' is horizontal axis. axis=1 (or axis='columns') is vertical axis. To take it further, if you use pandas method drop, to remove columns or rows, if you specify axis=1 you will be removing columns.

Explanation:

answer: 2×10^-2kg

explanation: density= mass per volume

vol=mass/density

converting to s.i units we have;

3÷1000kg = 0.003

1.5÷100m = 0.15

0.003/0.15 = 0.02kg