Question

if the direction of a moving car change and its speed remains constant, which quantity must remain the same

Answer 1

Is this with reference to UCM?

Answer 2

look the momentum of the car changes
then the velocity of the car changes
and of course the position of the car changes
i think that there's only one quantity that will not change and it is the car's mass(i know it's illogical but all the other quantities are changing)
:)