A car purchased for 17,000 is expected to lose valuse according to the straight line depreciation model y ?

The car will always have value. The equation is too simple. It doe not take into account for desirability, whether or not the car is going to stop being produced, and the fact that there is no car with the value of zero dollars. A car will always at least be worth its weight in scrap metal. That equation would make the car worth a negative amount in the future. That means the seller would have to pay someone to take the car.

Cars do not depreciate according to a straight-line model and they never lose all value. Even an old worn-out car has junk and parts value.

Every car's depreciation rate is different, according to it's make, model, condition, mileage, accident history, recall history, and the laws of supply and demand for that vehicle, which can change frequently. For example, when gas prices were high, large trucks and SUVs experienced an accelerated depreciation rate. Therefore, there is no formula that can predict or even describe (after the fact) a car's depreciation.