1. Consider the following statements about Mitochondria:
(1) The Mitochondria are also called as the powerhouse of the cell.
(2) Only maternal mitochondria are passed on to the progeny but not paternal mitochondria.
Which of the statements given above is/are correct?
(a) 1 only
(b) 2 only
(c) Both 1 and 2
(d) Neither 1 nor 2
Answer: (c) Explanation: The mitochondria are the double membrane-bound organelle found in almost all eukaryotic organisms. It is one of the most important organelles of the cell and performs various biological processes such as Adenosine Triphosphate (ATP) Synthesis, ion homeostasis calcium storage and regulation of cell death pathways. They are also known to possess their own genome. Mitochondria generate most of the cell’s supply of ATP, used as a source of chemical energy. Therefore, it is also called as the powerhouse of the cell. A prokaryote is a unicellular organism that lacks a membrane-bound nucleus (Karyon), mitochondria, or any other membrane bound organelle. Only maternal mitochondria are passed on to the progeny as researchers have found that the transmission of paternal mitochondria or father’s mitochondria is an evolutionary disadvantage. Hence, both statements are correct.
Source: NCERT Science Class IX – Chapter 5, page no. 64-65.
2. Which of the following statements is incorrect regarding the object moving in a circular path with uniform speed?
(a) This motion is called as uniform circular motion.
(b) This is an example of accelerated motion.
(c) At all instances, the object is moving tangent to the circle.
(d) None of the above.
Answer: (d)
Explanation: Statement (a) is correct. Uniform circular motion can be described as the motion of an object in a circle at a constant speed. Statement (b) is correct. As an object moves in a circle, it is constantly changing its direction. Accelerating objects are objects which are changing their velocity - either the speed (i.e., magnitude of the velocity vector) or the direction. Therefore, an object moving in a circle is accelerating. Statement (c) is correct. Since the direction of the velocity vector is the same as the direction of the object's motion, the velocity vector is directed tangent to the circle as well. Therefore, at all instances, the object is moving tangent to the circle. Hence, option (d) is the correct answer.
Source: NCERT Science Class IX – Chapter 8, page no. 110
3. Consider the following statements:
Assertion (A): We fall in the backward direction when a moving bus brakes to a stop and fall forwards when it accelerates from rest.
Reason (R): Inertia makes an object to resist a change in its state of motion.
Select the correct answer using the code given below:
(a) Both (A) and (R) are true and (R) is the correct explanation of (A).
(b) Both (A) and (R) are true but (R) is not the correct explanation of (A).
(c) (A) is true but (R) is wrong.
(d) (A) is wrong but (R) is true.
Answer: (d) Explanation: Newton’s first law of motion states that an object remains in a state of rest or of uniform motion in a straight line unless compelled to change that state by an applied force. In other words, all objects resist a change in their state of motion. Assertion (A) is NOT correct and Reason (R) is correct. We tend to remain at rest with respect to the seat until the driver applies a braking force to stop the bus. With the application of brakes, the bus slows down but our body tends to continue in the same state of motion because of its inertia. A sudden application of brakes may thus cause injury to us by impact or collision with the panels in front as we fall forwards. Similarly, when bus accelerates, we tend to move in backward direction.
Source: NCERT Science Class IX – Chapter 9, page no. 116
4. Consider the following statements:
(1) There is no change in the velocity of falling objects.
(2) The weight of an object is constant and does not change from place to place.
Which of the statements given above is/are correct?
(a) 1 only
(b) 2 only
(c) Both 1 and 2
(d) Neither 1 nor 2
Answer: (d) Explanation: Statement 1 is incorrect: We all know that an object experiences acceleration (g) during free fall. This acceleration experienced by an object is independent of its mass. This means that all objects hollow or solid, big or small, should fall at the same rate. As g is constant near the earth, therefore from equation v=u + gt, velocity is increased or decreased depending on the direction of velocity of the object. Statement 2 is incorrect: The earth attracts every object with a certain force and this force depends on the mass (m) of the object and the acceleration due to the gravity (g). The weight of an object is the force with which it is attracted towards the earth. That is, F=m*g. The mass of an object remains the same everywhere, that is, on the earth and on any planet whereas its weight depends on its location because g depends on location. For example, the weight of the object on the moon is approximately one-sixth of the weight of the same object on earth.
Source: NCERT Science Class IX – Chapter 10, page no. 135-136
5. Which of the following is/are applications of the 'Archimedes’ Principle'?
(1) Designing ships and submarines
(2) Lactometer
(3) Hydrometer
(4) Hot air balloon
Select the correct answer using the code given below:
(a) 1 and 2 only
(b) 2 and 3 only
(c) 1, 2 and 3
(d) 1, 2, 3 and 4
Answer: (d) Explanation: Archimedes’ Principle states that “When a body is immersed fully or partially in a fluid, it experiences an upward force that is equal to the weight of the fluid displaced by it”. Applications of Archimedes’ principle:
• Designing ships and submarines: A submarine has a large ballast tank, which is used to control its position and depth from the surface of the sea. A ship is constructed in a way so that the shape is hollow, to make the overall density of the ship lesser than the sea water. Therefore, the buoyant force acting on the ship is large enough to support its weight.
• Lactometer which are used to determine the purity of a sample of milk.
• Hydrometer which are used for determining density of liquids
• Hot Air balloon: The atmosphere is filled with air that exerts buoyant force on any object. A hot air balloon rises and floats due to the buoyant force (when the surrounding air is greater than its weight). It descends when the balloon's weight is higher than the buoyant force. It becomes stationary when the weight equals the buoyant force.
• Fishes: Certain group of fishes uses Archimedes’ principles to go up and down the water. Hence, option (d) is the correct answer.
Source: NCERT Science Class IX – Chapter 10, page no. 142