Doing this on clay Would add Kgs. If this was done on Fiber, That Would Be Beneficial to Save Weight and That Metal Too ! further making this more light
For the dependent variable for the gun vs the lawn mower... should be the "force created be the object" (gun/mower) NOT the angle the rig arm went up... I believe that the rig arm is the tool used to capture the force. Your hypothesis does not mention a rig arm...You all talk about force. So in my opinion this answer needs to be corrected.
That's a pretty remarkable result, but I'd like to know more about the method. Do we know if they controlled for the car being fully warmed up (engine, coolant, oil, transmission, bearings, tyres, etc.)? How many runs did they do, and did they drive in both directions? Did they have some way of locking the accelerator pedal to a fixed position?
I like how they half test something and think they've got actual results. I dont know if they balanced out the weight of the added clay, but they increased the size, which adds wind resistance! Also, increasing surface area while adjusting the weight would affect momentum. They really need to get over their smugness. They do this for a living and dont factor in the most fundamental things