Many military submarines are powered by on-board nuclear reactors. this type of energy source is favored because a. they can be converted into nuclear weapons at a moment's notice for use in wartime b. they can be easily replenished even when the submarine is submerged in deep waters c. they supply a lot of energy but do not take up a lot of space d. they are 100% efficient and do not produce any form of waste

The answer is; C

Nuclear reactors are small and lightweight (ratio of size to power generated) and provide energy reliably compared to other sources. They can carry their own weight by many folds ration. This is why they are also muted as the ideal source of energy in space exploration.

think about the oscillation of the toy shown in the video. when the toy is at the highest point of its motion, its velocity is zero and its acceleration is negative.

air exerts forces on falling objects near earth’s surface.

explanation:

the term 'free falls' refer to object that are falling towards the earth, in a situation in which gravity is the only force acting on the object.

for an object in free fall, the acceleration is constant (g, the gravitational acceleration), and so the velocity of the object constantly increases.

for objects near earth's surface, there is always another force acting on the object: the resistance due to the air. this force is opposed to the direction of fall of the object, and it is proportional to the velocity of the object, so as the object falls down, this force increases up to a point when it balances the force of gravity, and the object continues its motion at constant velocity (called terminal velocity). since in this case gravity is not the only force acting on the object, we are not in a situation of free fall.