No, an external force is not required for constant speed. The only thing that changes is direction due to magnetic field. So the velocity keeps changing but the speed will remain constant. Hence we do not need an external force to retain this speed.
Well I think it will be needed.
Yes, maybe you are right. But there is no path for current. It isn't a closed circuit so since current will be zero so force due to magnetic field will be zero and so i think no external force should be required.
Answer given is NO
Yes @Vishnu_Dalai u r right.