A bike traveling at 20km/h on a flat roadway stop pedaling.Make a diagram showing the forces acting on the coasting bike and rider.using newton's second law ,explain how the bike's motion change

SOURCE: Why the potential energy is unlimited?

Potential energy is unlimited simply because it's not used yet.
Once you start using it, it eventually ends.

SOURCE: 2002 Buick Park Ave gas pedel sticks

I would inspect the throttle cable first of all. They do have a braded cable which can break a strand and bind at areas inside the surrounding cable housing. It would be easiest to remove it from the throttle body and work it freely. That way you can tell if it binds up. Have some one push and pull up the gas pedal as well to inspect. You will know if this is the problem your having. Also lube the cable if you think it is still good to reuse

SOURCE: The brake pedal went to

just because you installed a new part doesnt mean its not defective....pull the wheels off and check to see if the pistons move freely in the calipers(remove calipers and try to press in with channel lock plyers). see if rear wheel cylinders are working with drums on , have someone press the brakes and you turn the drums.