You are travelling at constant speed in an airtight car with a
balloon floating motionless next to you. Suddenly, you slam
on the brakes so as to stop the car quickly. During decceleration,
with respect to the car the balloon
(a) moves forward; (b) remains motionless;
(c) moves backward; (d) can move forward or backward.
The Attempt at a Solution
The correct answer is c, that it moves backwards. Can someone explain why?