You mean to say "can a vehicle change gears from 5th to reverse on it's own while moving?" I have never heard any car doing so. You could do it yourself though.
This is what would happen:
If it's a manual transmission car: if the car is moving in 5th gear, you won't be able to slot the lever in reverse. You'll hear a grinding sound though.
If it's an automatic transmission: Depends on which type of automatic transmission vehicle it is (planetary gearbox, continuously variable transmission, automated manual transmission, dual clutch transmission.) Almost all automatic transmission cars will have their gearboxes damaged if reverse is slotted at speed. I have heard of a case where a car with a dual clutch gearbox was completely made dysfunctional when someone accidentally slotted reverse while moving at speed.
It’s highly unlikely. While it is possible for a car to pop out of gear unintentionally, there is a centering spring which will pull the selector lever to the center of the neutral pattern (between 3rd and 4th gear on most 5 and 6 speed transmissions). If you press the clutch and apply pressure to take the selector out of gear, it will move to this position on it’s own, without any left/right pressure required.
Most transmissions have a lockout feature to prevent accidentally selecting Reverse when intending to shift from 5th to 4th. Sometimes there is a physical lockout requiring you to press up or down on the shifter or raise a collar/press a button. On cheaper cars, there is extra resistance required to shift into reverse. Even if you use the lockout or overcome the resistance, it would not be possible to get the gears in the transmission to mesh together unless the car is stopped.
No It cant , If you try to put the car from 5th gear to reverse there be a large cranking sound and the gear will not mesh but if you further push it harder there are chances that you may wear out the gear.
As per the design of gear box there is an idler gear in between the reverse gear and forward drive gears to mesh the idler gear the car should be at stand still other wise it wont mesh, So its not possible that car will move from 5th to reverse accidentally unless warning you by a cracking sound.