[mayshine]

to make it more obvious

set g=10, m = 10 , back force = 50

first plane mass = 2m
second plane mass = 1m

F=ma

a1: a2
= (2m*g-backforce)/2m : (m*g-backforce)/m
=150/20:50/10
=7.5:5

a1 is 50% faster