Cambridge International AS & A Level Physics Coursebook … Draw the displacement–time graph for the girl from t = 0 to t = 12 s. [1] b On the same graph axes, draw the displacement–time graph for the boy. [2] c Using your graph, determine the value of t when the boy catches up with his sister. [1] [Total: 4] 9 [3] A student drops a small black sphere alongside a vertical scale marked in centimetres.