In a conceptual question Hewitt asked what
happens to the speed of an open freight car
(increases, decreases or remains the same)
when it rolls friction-free along a horizontal
track while a pouring rain falls vertically.
The expected answer is: "speed decreases
as water accumulates in the car because the
momentum must be conserved." What is a
good name for a force responsible for the
change in speed?
Ludwik Kowalski