Can an object be accelerated if it is moving with constant speed? If yes, give example.
Yes, surely! For example, a car is moving with a constant speed for some time. Then driver pushes the gas pedal and the car accelerates. If you mean that object is accelerated when speed is constant, well yes, that is possible in the sence that magnitude of the speed is constant. For example, the object moves along the circle. The magnitude of the speed is constant though its direction is not and that's why acceleration is not zero.