A 2,000-kilogram automobile accelerates horizontally to a speed of 20 m/sec. The change in its potential energy is: (Hint: the question did not ask you for the potential energy. It asked you how much the potential energy changed when it increased speed)

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no

sodium is solid at rt

it's when something is going so fast it makes a loud noise, breaking the sound barrier, for example: a jet makes a loud noise, not only cause of the jet but because they reached a point where they went so fast that you can year the noise from various parts, kinda like a police car, lets say the car was going   so fast that you hear the siren of the cop car right next to you, but the car is probably a mile a way, it's cos the siren was next to you a few seconds if you understand me