A pickup truck is being driven down the highway carrying eight 100 gallon fish tank full of water. A hole is punctured in each t
ank and the water flows out of the tanks and truck to the ground. If the driver maintains the same pressure on the gas pedal, and the road stays flat and level, what happens to the velocity of the truck and which conservation law applies?
The velocity of the vehicle would increase because the the tanks (when filled with water) must have exerted a force which would reduce the velocity of the vehicle at a certain pressure on the gas pedal. Note that force equals mass multiplied by acceleration; as the mass decreases, so the force decreases. Thus, when the mass exerted by this tanks (on the vehicle) decrease as a result of the hole punctured in them, the force exerted by the tanks would also decrease causing an increase in velocity of the pick up truck when the same pressure is applied on the gas pedal throughout (before and after the puncture).
The conservation law that applied here is the law of conservation of energy which states that energy can neither be created nor destroyed but can be transformed from one form to another. This is because the energy the vehicle used in carrying the load (the tanks) was transformed to the energy that resulted in increasing it's velocity (no new energy was formed as the pressure on the gas pedal remained the same).
