To hear a train approaching from far away, why is it more convenient to put the ear to the track?

If you want to hear a train approaching from far away,it is more convenient to put the ear to the track.This is because sound can travel through railway track (solid ) faster than through air.

33: i think it’s b

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