## acceleration and water height

I'm having trouble with this problem here.

A U-shaped tube with a horizontal portion of lenght L contains a liquid. What is the difference in height between the liquid columns in the vertical arms if the tube has an acceleration toward the right?

There must be a net force to the left that presses the liquid to the left. In the right column there must be a pressure greater than the atmospheric pressure. But I don't know how to relate the lenght of the tube to the answer. Could someone please give me a clue how to solve this.
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 why must there be a force to the left? acceleration is to the right. what makes you think that there is pressure greater than atm. on the right. could you explain your logic.
 The tube accelerates to the right. The water goes to the left, so there must be a force pressing it to the left. I know its not really a force, but It helps thinking of it that way. When you drive a car in a circle your body gets pressed to the sides. Your body is not in a an inertial frame of reference neither is the water. Is this not true?