Free Scientific Reasoning MCQs with Answers

51. Which of the following reaction involves the greatest change in enthalpy?

• A. Condensation
• B. Nuclear fission
• C. Reduction
• D. Combustion

Explanation: Nuclear fission involves the greatest change in energy as indicated by the amount of energy released which is used to run nuclear power plants or cause atomic explosions.

52. Which of the following is a spontaneous reaction at room temperature?

• A. Lighting a matchstick
• B. Boiling water
• C. Removing sodium chloride from water
• D. Increasing the height of a ball from the ground to an elevated table

Explanation: A spontaneous reaction is one that proceeds on its own once initiated. Lighting a matchstick is spontaneous after the initial ignition because the chemical reaction sustains itself without needing additional energy. In contrast, boiling water at room temperature, separating salt from water, and lifting a ball all require continuous or external energy inputs, and are therefore non-spontaneous processes.

53. Why do ceiling fans accumulate dust even though they move so quickly?

• A. Dust sticks to the rust in fans
• B. The electrostatically charged fan blades attract dust particles
• C. The dust settles in and sticks to fans when they are not moving
• D. The momentum of the fan is so high that the dust particles which have low inertia are instantly caught in the motion of the blades and adopt the motion of the blades

Explanation: The correct answer is that the electrostatically charged fan blades attract dust particles. As the fan blades move rapidly through the air, they generate friction with air molecules. This friction can lead to a static charge building up on the blades, which then attracts dust particles. This phenomenon occurs even when the fan is in motion, making this explanation the most plausible. The other options do not account for the electrostatic attraction: rust is not a significant factor, dust settling when stationary doesn't explain accumulation during motion, and momentum does not cause dust to adhere.

54. Order the following steps to separate a mixture of sodium chloride, sand and iron.I- Mix in waterII- EvaporateIII- hold a magnet bar above the mixture/solutionIV- Filter and dry filtrate

• A. I>II>III>IV
• B. II>III>IV>I
• C. I>III>IV>II
• D. III>I>IV>II

Explanation: To obtain dry iron, we first hold a magnet above the mixture. We then mix the remaining salt and sand into water. We filter out and dry the sand. Following this, we evaporate the water to obtain dried sodium chloride.

55. Why does the hair on our arms get raised when it is brought near a television screen?

• A. The magnet of the television screen attracts the magnetic hair
• B. The electrostatically charged television screen induces a charge on our hair and attracts it.
• C. The television screens have a glue which makes our hair stick to them
• D. We get goosebumps from standing that close to a screen as part of a reflex action

Explanation: Following use, TV screens attain an electrostatic charge which induces a charge on our hair and attracts it. The same phenomenon is responsible for dust sticking to television screens following use.

56. Why does our hair get messy after we pull off a cap/hat?

• A. The hair clings to the fibers in the cap causing them to be disoriented
• B. The electrostatic interactions between the hair and the cap cause the hair to become messy
• C. Sudden exposure to increased sunlight damages the hair
• D. None of the above

Explanation: friction between the cap and hair yields electrostatic charges leading to the hair being attracted to the cap and as a result, becoming messy

57. In which of the following cases does the force do no work?

• A. Lifting a box from the ground
• B. Pushing a box
• C. Pulling a box using a string
• D. Carrying a box to a different room

Explanation: Work is defined as the component of the force parallel to the displacement multiplied by the magnitude of the displacement. In the scenario of carrying a box horizontally across a room, the force exerted is vertical, while the displacement is horizontal. Since there is no force component in the direction of displacement, no work is done in this case. Conversely, in the other scenarios (lifting, pushing, and pulling), the force applied has a component in the direction of displacement, resulting in work being done.

58. In which of the following is work being done?

• A. Jack carrying a bucket of water along a horizontal road
• B. A skydiver falling with uniform velocity towards the ground
• C. Sarah walking up the staircase
• D. Asad swinging a marble tied to a string at uniform speed

Explanation: Work is defined as the force applied on an object causing displacement in the direction of the force. In option C, Sarah walking up the staircase involves applying a force against gravity, resulting in vertical displacement, hence work is done. In option A, Jack's vertical force does not cause horizontal displacement, so no work is done. Option B describes a skydiver with balanced forces, meaning no net force and thus no work done. In option D, the force is centripetal and perpendicular to the motion, so no work is done.

59. In which case is no work being done?

• A. Pulling a rubber band
• B. Climbing a ladder
• C. A phone thrown down from the balcony
• D. A carton sliding on a frictionless horizontal floor

Explanation: Since there is no frictional force, and the carton is experiencing no other net force, no work can be done

60. The figure shows Sara (left) weighing 50kg and Afsana (right) weighing 40 kg using a seesaw together. The seesaw is 2m long. How much farther should Afsana and Sara be from the edge of the seesaw on their respective sides for the beam to be balanced?

• A. Afsana = 15cm, Sara= 40cm
• B. Afsana = 40cm, Sara = 52cm
• C. Afsana = 40cm, Sara = 15cm
• D. Afsana = 20cm, Sara = 3cm

Explanation: So, Afsana is 40 cm away from the midpoint, and Sara is 52 cm away from the midpoint.Since the seesaw is 2m (200 cm) long, the midpoint is at 100 cm. To balance the seesaw, the moments about the midpoint must be equal.Afsana's moment = 40 kg × 40 cm = 1600 kg-cmSara's moment = 50 kg × 52 cm = 2600 kg-cmTo balance the seesaw, Afsana needs to move away from the midpoint until her moment equals Sara's moment.Let's calculate the distance Afsana needs to move:New distance = (2600 kg-cm) / (40 kg) = 65 cmSo, Afsana needs to move 25 cm (65 cm - 40 cm) farther away from the midpoint to balance the seesaw.Answer: Afsana needs to move 25 cm farther away from the edgeof the seesaw. To determine if the given distances of Afsana and Sara will create equilibrium on the seesaw, we need to check if the sum of the clockwise moments is equal to the sum of the anticlockwise moments.Anticlockwise moment (due to Sara) = Clockwise moment (due to Afsana)We need to use the distance from the pivot to calculate the momentum. We know that the seesaw has a total distance of 2m, and each arm will be 1m so, the distance from the pivot= 1 - 0.40 = 0.60 m for Afsana and 1 - 0.52 m = 0.48 m for Sara (convert cm to m by dividing by 100)Weight of Sara × Distance from the pivot to Sara = Weight of Afsana × Distance from the pivot to Afsanamg x d = mg x d50 x 10 x 0.48 = 40 x 10 x 0.60240 = 240 This option is our correct answer since the clockwise moment equals the anticlockwise moment. Sara and Afsana are 52cm and 40cm away from the edge of the seesaw respectively.