You are riding on your bike and stop pedaling, coasting along the road. eventually, your bike slows down and stops. what happened to the energy of your motion when your bike stopped?

When still rolling your bike had kinetic energy, or energy in the form of motion. The forces resisting this motion--a mixture of many factors including air resistance, tire friction, friction in the hubs of the wheels, etc ... - - eventually decrease the kinetic energy of the bike to zero as it reaches a complete stop.