Why ac is used in india instead of dc? why dc can't be used for the long distance transmission but ac can be used?

The 10-kg double wheel with radius of gyration of 125mm about o is connected to the spring of stiffness k = 600 n/m by a cord which is wrapped securely around the inner hub. if the wheel is released from rest on the incline with the spring stretched 225 mm, calculate the maximum velocity v of its center o during the ensuing motion. the wheel rolls without slipping

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Amajor difference radio waves, visible light, and gamma rays is the of the photons, which results in different photon frequencies and wavelengths