Free Scientific Reasoning MCQs with Answers

21. Pluto has a diameter of just 1,438 miles. It is made mostly of ice and frozen rock. It is very small and has an irregular orbit. It was originally classified as the ninth planet from the Sun, but it has been recategorized as a dwarf planet within the Kuiper belt. Which of the following is not a factual detail about Pluto?

• A. Pluto has a diameter of 1,438 miles.
• B. Pluto is made mostly of ice and frozen rock.
• C. Pluto has an irregular orbit.
• D. Pluto should be classified as a dwarf planet.

Explanation: D is the correct answer because it is not a factual detail about Pluto. It is a classification of Pluto that has been assigned by the International Astronomical Union based on a set of criteria that define what a planet is. Some scientists and members of the public may still consider Pluto to be a planet, but the current scientific consensus is that it should be classified as a dwarf planet within the Kuiper belt. Therefore, option D is not a factual detail about Pluto, but rather a categorization assigned to it.

22. Objects are attracted to one another by the force of gravity. Gravity is proportional to the mass-the amount of matter-objects have; gravity decreases as the distance between the objects increases. An object's weight is a measurement of the Earth's gravitational pull on the object. What happens to the mass and weight of a rocket as it travels beyond Earth's orbit?

• A. Its mass remains the same, and its weight increases.
• B. Its mass remains the same, and its weight decreases.
• C. Its mass decreases, and its weight decreases.
• D. Its mass increases, and its weight remains the same.

Explanation: B is correct because weight is directly proportional to the gravitational force acting on an object, which decreases as the distance between the objects increases. As the rocket travels beyond Earth's orbit, it moves away from the gravitational pull of Earth, and therefore its weight decreases. However, the mass of an object remains constant, regardless of its location in space.

23. You run an experiment to test which brand of food your dog prefers. You offer her three different brands of food at each meal, presenting them all at the same time (so that she does not just prefer the one that comes first!). Three weeks of data collection indicate that she ate Brand C more often than Brand A or Brand B. What can you conclude from these results?

• A. Your dog preferred Brand C but you do not know why
• B. Brand B was her second favorite food
• C. Brand C is the healthiest food
• D. Brand B and Brand A taste bad
• E. Brand C is the cheapest food

Explanation: The only conclusion that can be drawn from the given results is that the dog preferred Brand C over Brand A and Brand B. Therefore, the correct answer is A: Your dog preferred Brand C but you do not know why. None of the other options can be inferred from the given information.

24. "The World Health Organisation has recorded 184 human cases of the H5N1 strain of bird flu, all of them caused by contact with infected birds. That 103 of these have resulted in death indicates how dangerous this virus is, and no vaccine has yet been developed. For there to be a worldwide epidemic of H5N1 amongst humans, it would have to be possible for the virus to be passed easily from one person to another. Unlike normal influenza, H5N1 can only bind to receptors deep in the lungs. As a result, it cannot multiply in the upper respiratory system and thereby be transmitted by sneezing and coughing. So it cannot be transmitted easily between people. Influenza viruses can mutate, and thus possibly change the way in which they infect victims." Which of the following can be drawn as a conclusion from the passage above?

• A. Unless a vaccine is developed, many more people will catch the H5N1 strain of bird flu.
• B. If H5N1 mutates, there is likely to be a worldwide epidemic amongst humans of this strain of bird flu.
• C. Unless H5N1 mutates, a worldwide epidemic amongst humans of this strain of bird flu is unlikely.
• D. If a person has no contact with birds, they are unlikely ever to catch the H5N1 strain of bird flu.
• E. None of the above

Explanation: B is the correct conclusion that can be drawn from the passage, as it is stated that influenza viruses can mutate and possibly change the way in which they infect victims, suggesting that a mutation in the H5N1 strain could potentially lead to a worldwide epidemic among humans

25. A ballet dancer of mass 80 kg and a wingspan of 80cm is executing a spin. She then folds her arms and brings them to within 20 cm from the central axis of her body. If she was initially making 3 rotations per second, how many does she make now?

• A. 35 rotations per second
• B. 48 rotations per second
• C. 15 rotations per second
• D. 6 rotations per second

Explanation: To solve this problem, we use the principle of conservation of angular momentum, which states that the initial angular momentum must equal the final angular momentum in the absence of external torques. Mathematically, this is represented as:I1ω1 = I2ω2where I is the moment of inertia and ω is the angular velocity. The moment of inertia for a rotating body like a dancer is proportional to the square of the radius (r), so I = mr2. When the dancer folds her arms, the radius decreases from 80 cm to 20 cm, a factor of 4 reduction. Consequently, the angular velocity increases by the square of this factor, that is, 42 = 16 times. Thus, the new angular velocity is 3 rotations per second × 16 = 48 rotations per second.Options A (35 rotations per second), C (15 rotations per second), and D (6 rotations per second) provide incorrect results because they fail to apply the correct factor of increase in angular velocity based on the reduction in radius.

26. The small gear has 10 teeth and the big gear has 50 teeth. When the small gear rolls around the big gear, how many times will the arrow return to its initial orientation (pointing upward)?

• A. 5 times
• B. 10 times
• C. 6 times
• D. 8 times

Explanation: To determine how many times the arrow on the small gear returns to its initial orientation, consider two factors: the rotations from rolling along the equivalent distance of the big gear's circumference, and the additional rotation due to the gear's circular path.First, the small gear with 10 teeth rolls around the big gear with 50 teeth. If the small gear were rolling on a flat surface covering a distance equal to the big gear's circumference, it would rotate 5 times, as 50 (teeth of big gear) divided by 10 (teeth of small gear) equals 5. However, because the small gear is not only rolling but also rotating around the big gear, it makes one additional rotation due to the circular path it follows.Thus, the arrow returns to its initial orientation 5 + 1 = 6 times. The other options incorrectly account for the rotations by either ignoring the additional circular rotation (5 times) or adding unnecessary rotations (10 times and 8 times).

27. An observer on the ground sees an eagle flying towards thep east at 15m/s chasing a hummingbird flying at 5 m/s. He approximates that the mass of the eagle is 4 times that of the hummingbird. If the eagle catches the hummingbird and continues to fly with the same thrust from its wings, what speed with the observer see them moving at?

• A. 10m/s
• B. 13m/s
• C. 16m/s
• D. 7m/s

Explanation: Let mass of hummingbird=m1. Mass of eagle = m2 =4m1 By law of conservation of momentum;M1v1 + m2 v2 = (m1+m2)x5m1 + 15(4m1) = (m1 +4m1)x65m1 = 5m1 xX = 13

28. Why is the pupil of the human eye black?

• A. The pupil appears black because it is made of dark-colored tissues.
• B. The pupil can appear in different colors depending on the light conditions.
• C. The pupil is a hole that allows light to enter, and it appears black because the light is absorbed or scattered inside the eye.
• D. The vitreous humor behind the pupil is black, causing the pupil to appear black.

Explanation: The pupil is an opening in the center of the eye's iris that allows light to enter and reach the retina. It appears black because the light that enters is absorbed by the retina or scattered inside the eye, making it difficult for the light to escape back out through the pupil. This absorption and scattering of light give the pupil its characteristic black appearance. The other options are incorrect because they either misidentify the nature of the pupil or suggest incorrect reasons for its appearance.

29. Why does the burning of a tire yield black smoke while burning stoves in homes rarely produce smoke?

• A. Burning tires release particles that break off due to heat and create the appearance of black smoke.
• B. The heat from the fire melts tires and the evaporated material contributes to black smoke.
• C. Combustion of heavy fuels like tires results in incomplete combustion, producing elemental carbon that appears as black smoke.
• D. None of the above options are correct.

Explanation: The correct answer is that combustion of heavy fuels like tires results in incomplete combustion, producing elemental carbon that appears as black smoke. Tires are made of materials that do not combust fully under regular fire conditions, leading to the production of soot. This soot is composed of tiny carbon particles that absorb light, giving the smoke its black appearance. In contrast, home stoves usually burn fuels designed to combust more completely, often producing less smoke. Options A and B are incorrect as they do not accurately describe the cause of black smoke, and Option D is incorrect because there is a correct explanation provided.

30. When driving a car around a corner, why do we feel as if we are thrown away from the corner?

• A. There is a force acting on you away from the center of the turn called centrifugal force which gives this feeling.
• B. Your inertia wants you to keep moving in a straight line.
• C. Your body offers a reaction force to the centripetal force of the turn away from the center.
• D. The turn causes a pressure difference on either side of the car which causes you to move towards the region of low pressure which is away from the center of the curve.

Explanation: When you drive around a corner, your body wants to continue in a straight line due to inertia, as described by Newton's first law of motion. This creates the sensation of being 'thrown' outward. However, as the car turns, the door or seat applies a centripetal force towards the center of the curve, altering your path to match the car's. This force is what actually keeps you moving in a curved path.Option A is incorrect because centrifugal force is a perceived effect, not an actual force. Option C misunderstands the nature of action-reaction pairs, and option D incorrectly attributes the sensation to pressure differences, which are not the cause in this scenario.