Correct Answer: A

Rationale: According to Newton's second law of motion, acceleration is directly proportional to the force acting on an object when the mass is constant. Therefore, if the force acting on an object is increased while the mass remains constant, the acceleration of the object will also increase. This relationship is described by the formula F = ma, where F is the force applied, m is the mass of the object, and a is the acceleration. When force increases, acceleration increases, and vice versa, as long as the mass stays the same. Choice B (Acceleration decreases) is incorrect because acceleration and force have a direct relationship. Choice C (Acceleration remains constant) is incorrect because acceleration changes in response to changes in force. Choice D (Acceleration becomes zero) is incorrect because increasing force does not make acceleration zero; it actually increases it.

Correct Answer: A

Rationale: Neon (Ne) and Helium (He) belong to Group 18 (Noble Gases) because they have complete and stable outer electron shells. The stability of these outer electron shells is due to the balance of attractive forces between the positively charged protons in the nucleus and the negatively charged electrons in the outer shell. This balance is maintained by the electromagnetic force, which is responsible for holding atoms together and determining their chemical properties. Gravity (Choice B) is a force of attraction between objects with mass and is not responsible for the stability of electron shells. The strong nuclear force (Choice C) and weak nuclear force (Choice D) are forces that act within the nucleus of an atom and are not directly related to the stability of outer electron shells in determining an element's group in the periodic table.

Correct Answer: C

Rationale: The correct answer is C: Mitochondria. The energy for most cellular processes is produced in the mitochondria through the process of cellular respiration. Mitochondria are often referred to as the powerhouse of the cell because they generate ATP, the energy currency of the cell. This process involves the breakdown of glucose molecules to produce ATP, which fuels various cellular activities. Choices A, B, and D are incorrect. The nucleus is responsible for storing genetic material and controlling cell activities, not energy production. The cytoplasm is where various cellular activities take place, but it is not the primary site for energy production. Ribosomes are involved in protein synthesis and do not generate energy for cellular processes.

Correct Answer: A

Rationale: The main function of the stomach is to store food, churn it, and break it down into smaller pieces through mechanical digestion. This process is facilitated by the mixing of food with gastric juices, including stomach acid. The mechanical breakdown in the stomach helps initiate the digestion of food before it progresses to the small intestine for further digestion and nutrient absorption. Absorption of nutrients into the bloodstream primarily occurs in the small intestine, not the stomach. Enzymes that aid in digesting food are primarily produced in the pancreas and small intestine, not in the stomach. The elimination of waste products from the body mainly occurs through the large intestine and rectum, not the stomach.

Correct Answer: B

Rationale: Kinetic energy is directly proportional to the square of the velocity of an object according to the kinetic energy formula (KE = 0.5 * m * v^2). When the velocity is doubled, the kinetic energy increases by a factor of 2^2 = 4. Therefore, the kinetic energy quadruples when the velocity of an object is doubled. Choice A is incorrect because halving the kinetic energy would be the result if the velocity was halved, not doubled. Choice C is incorrect because doubling the velocity would result in a fourfold increase in kinetic energy, not just a double. Choice D is incorrect because kinetic energy is directly related to the velocity of an object, so if the velocity changes, the kinetic energy changes accordingly.