Q. Explain what is meant by nuclear fission?
Ans. The splitting of the nucleus of an atom into nuclei of lighter atoms emitting neutrons and accompanied by the release of a large amount of energy is called nuclear fission. Fission may be spontaneous or it may be initiated by the impact of neutrons.
Q. What is nuclear fusion?
Ans. A thermonuclear reaction in which nuclei of lighter atoms combine to form nuclei of heavier atoms and a large amount of energy is released. For example, deuterium atoms combine to produce helium atoms. Fusion reactions are considered to be endless source of energy given out by the Sun.
Q. Under what conditions do a feather and a lump of lead fall at the same rate
Ans. A feather and a lump of lead will fall at the same rate when they fall freely under vacuum.
Q. What fact or law is associated with the following occurrence : if you jump out of a moving train you will be carried forward in the direction of its movement, unless you exercise some force to prevent it.
Ans. This fact is associated with Newton’s first law of motion. According to this law, everybody continues in his state of rest or uniform motion in a straight line, unless he is compelled by some external force to change that state. The person jumping out of a moving train is carried forward in the direction of the train, because the person himself is in motion sharing the velocity of the train and will continue in his state of uniform motion, unless he exercises some force to prevent it.