Very interesting. I see a similar concept of nitroboosters here. Maybe if the balloon is larger- it would gain greater speed and greater distance as i see here in the video that the air runs out before the troll car reaches its terminal velocity. ( because if i pause the video 1 sec apart. the distance d1 in first second t1 is shorter than d2 in t2.). Or maybe use a thinner straw - low speed and maybe longer distance. Although I am a medico , I too am a huge fan of physics. I hope to post the project that i am on during my free time with my friends who are in aeronatics. Regards.