Turn the Coke bottle upside down in the center of your poster board. Trace the circumference of the bottle top, then cut out the circle with scissors. Cut a straight line from the middle of one side of the circle, to the edge of the poster board.
Shape the poster board into a cone. Staple the cone together along the seam. Trim the bottom of the poster board until it is the exact height of the Coke bottle so it can fit over the bottle during your experiment.
Pour out about 1/3 of the Coke from your bottle, then pour in 2 tbsp. vinegar. Put the lid back on Coke, then put the cone over the top of your Coke bottle. Set the bottle and cone in the center of your sturdy board.
Paint the poster board cone with your acrylic paints until it looks like a mountain. Use brown as your base coat and add color accents with your red and green paints. Let dry.
Set your two 8 1/2-by-11-inch sheets of paper directly on top of each other and roll the sheets into a funnel. Tape the funnel along seam to secure.
Mix your 1/2 pack of Mentos and baking soda in your cup. Take off the bottle top and insert the funnel.
Pour the contents of your cup into the bottle as quickly as possible and yank out the funnel immediately.