Atomic number Z = number of protons. Defines chemical element. Mass number = protons + neutrons. Isotopes same Z, different neutrons. Isobars same A, different Z.
Explanation:
Constant velocity implies zero acceleration, net force = 0 by Newton's first law. Engine force balances friction and air resistance. Net force zero, not necessarily zero forces.
Explanation:
Law of reflection: angle of incidence = angle of reflection, both measured from normal. So 30°. If angle with mirror is given, convert to normal. Always equal for smooth surfaces.
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