Hi:) is question 6 correct?

-- When you see the words "uniform speed", that means the car's speed is not changing.  

-- Right under those words in the picture, there's a note to remind you that "uniform speed" also means "acceleration is zero".

-- The whole key to this question is to find out if you remember that acceleration and net force always go together.  

.==> If there's net force, then there's acceleration.

.==> If there's acceleration, then there's net force.  

.==> If there's NO net force then there's NO acceleration.

.==> If there's no acceleration, then there's no net force.

-- In this picture, there's no acceleration, so there's no net force.

-- The driving force on the car is 2000N forward.

-- But the car's speed is not changing, so the net force on the car must be zero.

-- So that 'resisting' force pulling the car backwards must be 2000N. Then the net force on the car adds up to zero.

-- If the resisting force pulling the car backwards is not zero, then the net force on the car would not be zero, and the car's speed would be changing.

moving ball hits still ball. mover stops, hit ball moves. momentum transfer.