Will the car not start if filter is in backwards?

Yes, a filter installed backward can prevent a car from starting, or cause other serious problems. This is especially true for oil filters and fuel filters. They have a specific direction of flow, and reversing them will block the flow of the vital fluids they're designed to filter. This can lead to:

* No lubrication: A backward oil filter will prevent oil from flowing to the engine, leading to immediate and catastrophic engine damage if the engine is even attempted to be started.

* No fuel: A backward fuel filter will prevent fuel from reaching the engine, preventing the car from starting at all.

Air filters are less critical, though installing one backward might slightly reduce airflow and potentially impact performance. It's unlikely to completely prevent starting, however.