A 21 newton force keeps a 3 kg object in uniform circular motion. The speed of the object is 9 m/s. The magnitude of the centripetal acceleration is 3 m/s^2
7 m/s^2
27 m/s^2
30 m/s^2

You can watch static electricity in action by rubbing an inflated balloon against your hair. your hair will actually stand on its end! it does this because each hair becomes charged, and they all repel one another.