The diagram shows a marble falling through a liquid soap in a transparent container. Letters X (upwards) and Y (downwards) represent forces acting on the marble. The distance–time graph represents its motion: curving up from 0 to A, then straight from A to B.

1. aName force X. [1]
2. bName force Y. [1]
3. cWhat happens to the magnitude of force Y as the marble falls through the liquid soap? [1]
4. dExplain the motion of the marble in region AB in terms of forces X and Y. [2]

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