Hi, I'm a second year Design Engineering student. This year we're having some basic physics class. We're doing projects on potential energy at this moment. I'm having a problem with the following; The assignment: The teacher assigned us that only 6 Joules of potential energy may be used to make a contraption move as far as possible, this can be anything, a car, a paper plane, etc.. 1. The problem statement, all variables and given/known data I connected 5 rubber bands in series with on one side a weight (15 grams), on the other side some duct tape. The duct tape sticks to the ground while the weight is being tentioned. I let loose of the weight and the whole contraption (including rubber bands and duct tape) shoots away. I need to get to know the potential energy of a shot. 2. Relevant equations I calculated the spring constant by hanging a bottle of with water (545 grams) to the rubber bands in series, the rubber bands stretched out 25cm (50cm - 25cm) F= kx k= F/x k= 5,5N/0,25 k= 22Nm 3. The attempt at a solution Then I calculated the PE. This is my ACTUAL PROBLEM, I'm very sceptic about this one because it's seems too little.. (I'm not the best with physics or maths) PE= 1/2*k*x² PE= 0,5*22Nm*(0.25m)² PE= 0,6875 J A picture of the setup Is this a realistic/plausible result? Am I doing this right? The rubber bands I'm using are the typical office rubber bands. It would be nice if someone could help me out with this one. Thank you.