The precipitate is the barium sulfate, or 3) BaSO4. This is because it is a solid (as seen by the (s)), unlike the other aqueous product. The fact that it is a solid means that it is insoluble in water and therefore a precipitate.
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The force of static friction keeps a stationary object at rest. Once the force of static friction is overcome, the force of kinetic friction is what slows down a moving object.
The type of radiation that can penetrate through paper, but not through wood is called beta rays. Beta rays can penetrate paper and air, but a thin piece of alimony can stop it. Gamma can cut through anything except lead and many inches of concrete. Alpha can be stopped by paper and not penetrated. The correct answer is B.
The answer is evolution. When a specifies evolves over time they change and adapt to their environment.
W=mgh W=(20)(9.8)(1) w=196J