Graphs of Motion 3

With the two sliders in the bottom you can change the slope of the functions. You can change the distance of the blue and the red function on the x-Axis by moving the big red button. In this version you can't move the car and the bicycle.
Try to find the right functions for the following problem. If you are right, a text will appear. Martina and her little sister Kristina want to meet in Linz, which is 4 km from home. Kristina rides her bike and Martina follows by car 3 hours later. When do they meet in Linz? Why is this example unrealistic?