Click on the link to the Collision Carts interactivity and explore the simulation by clicking on "Launch Interactive." After you start the interactivity, pick a cart and put it on a track and slam it into a second cart. Change the mass and/or the velocity and repeat the experiment. Put two carts next to each other on the same track with a firecracker between them. Ignite the fuse and watch the carts fly apart when the firecracker explodes.
You can also use the following instructions to walk through the interactivity step-by-step:
The interactivity and activities are used with permission from The Physics Classroom.