How do you do this without taxing the first one?
If someone buys a truck to haul building materials to a building site, they are understandably not going to buy a separate vehicle just to haul 2 bags of groceries. But then how do you know what anybody is using it for the rest of the time? The list of legitimate purposes is unlimited. You're a homeowner who is into gardening and always bringing home mulch and saplings and renting landscaping equipment for projects. You're a retrocomputing enthusiast whose hobby requires you to be constantly transporting old mainframes. You're a parent who has to transport an entire junior varsity soccer team to practice every night.
How do you propose to distinguish any of these from someone who only buys a tank to carry home groceries?
But yes, truck used to haul building materials for a building site is the vehicle fulfilling its purpose and any replacement for that purpose being suboptimal.
Truck bought to haul 2 bags of groceries is not. Tax the second one.