英文 介系詞移位的問題?

1. We fall at a certain speed.
+ That speed has nothing to do with our weight.
= The speed at which we fall has nothing to do with our weight.
把第一句併入第二句時，形容詞子句與先行詞speed的關係是at which (= at that speed)

2. We received a complaint from a customer.
+ That customer was a professor.
= The customer from whom we received the complaint was a professor.
把第一句併入第二句時，形容詞子句與先行詞customer的關係是from whom (= from that customer)

What is the re-positioning of the prepositions?
(1)For fall---wt.---speed;
We do not fall at speed at our weight.
Weight/speed are surprised at the fall.
(2)A complaint from(prep) the professor(=customer).
We received a complaint from the professor.