It’s physical something you can physically do
Explanation:
Mass of bumper cars, 
Initial speed of car A, 
Initial speed of car Z, 
Final speed of car A after the collision, 
We need to find the velocity of car Z after the collision. Let it is equal to
. Using the conservation of momentum as :




So, the velocity of car Z after the collision is (-12 m/s). Hence, this is the required solution.
It is salt water because they are two things combined together.
1. your ear drums feel like they pop when you go deep enough under water. kinda feels like bricks. and it hurts if you stay under to long.
2. this could be a reaction from fluid pressure yes. can could be avoided by getting wax ear plugs however even with ear plugs going deep enough under water can still make your ears "pop" due to pressure but at high surfaces it would avoid that.
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