TheAntiSocialist's - Physics explanation questions thread

[TheAntiSocialist]

Math in physics is easy...there is no doubt about that.
But of course VCE physics isn't really  all about the maths...CONCEPTS in physics undoubtedly take precedence...
And so this is when I find it difficult  - when I encounter questions that require EXPLANATIONS
Most I know...and some I don't know...

Often that indicates that my concepts are not clear - or I just can't explain it intelligibly 

Any help will be greatly appreciated 

[TheAntiSocialist]

First up...here is a question I got from an exam ages ago...I think it's from 2003

Kim is driving a dodgem car. He is travelling at 2.0 m/s when he hits an oil patch and collides head on with the guardrail. The dodgem car has a spring-loaded bumper. After the collision the dodgem car rebounds directly backwards along the same line at a speed of 2.0 m/s. The mass of Kim and the dodgem car is 200 kg.
By doing calculations, show that the collision between the dodgem car and the guardrail satisfies the law of conservation of momentum. In particular, explain how momentum is conserved.

What I did:

1. I drew a diagram of Kim/car and the guardrail - then establishing direction (+ in the direction of the car's velocity)...
2. I then began labelling masses and velocities...
3. Did fine for dodgem car/person...

Then I looked at the guard rail...

 

Is there something to do with the spring bumper that I need to factor into solving my answer? I really dunno