Physics Olympics: Design System for Cable Car "Bomb" Drop

[xporcelainx]

Homework Statement

Drop the Bomb
a. design a system that attaches to a moving cable car. The system must drop a water balloon "bomb" on a large target while moving. Cable car is supplied.
[this was the information students were given.]

Homework Equations

The Attempt at a Solution

Any ideas? I'm pretty stumped myself. I though maybe some sort of removable bottom to the box, but the box has to keep moving the whole time. Since the zip line the car is traveling between is attached to two trees, my first thought was to have a removable door tied to a string tied to the tree. This string would be the same length as the distance from tree to target. The door would come off at the end of the rope, and balloon would fall.
Do you think this would work out? I'm just looking for some feedback. Thanks!

 

[Mindscrape]

Keep in mind that the balloon travels at the same speed as the car in the "x-direction."