fluid statics, (behaviour of lighter & heavier bodies in water) at constant acceleration

If a car filled with water is accelerated at uniform rate, and a heavy object is hanged by a string from the top of the car and a balloon with a string from the bottom of the car. What would be the direction of deflection of balloon & the heavy object. I would appreciate if someone could explain to me the phenomena of deflection, which would be helpful for me to better understand the topic please.