Class 9 Science Chapter 8: Force and Pressure MCQ with Answers (30 Questions)

The redesigned CBSE Class 9 Science paper allocates 40–50% of marks to objective questions (MCQs, true/false, fill-in-the-blanks). Unlike descriptive answers, MCQs test whether you can *recognize and distinguish* concepts instantly—a skill that separates 85+ scorers from 70-scorers. In Chapter 8, examiners test three layers: (1) definition recall ('What is pressure?'), (2) formula application ('If F = 50 N and A = 2 m², find P'), and (3) conceptual logic ('Why does a needle pierce cloth but a flat eraser doesn't?'). A single misread word in an option (e.g., 'increases' vs. 'decreases') costs you a mark. MCQs also eliminate vague answers—you either know the concept or you don't. Practicing 30+ varied MCQs trains your brain to spot distractors, manage time under pressure, and build pattern recognition across atmospheric pressure, buoyancy, and force scenarios.

**Q1.** Which of the following is an example of a push force? (A) Pulling a door open (B) Pushing a shopping cart (C) Stretching a rubber band (D) Throwing a ball **Answer:** (B) Pushing a shopping cart **Why:** Push forces move objects away; pull forces draw them closer. Pushing a cart applies force away from the person. **Q2.** Pressure is defined as: (A) Force × Area (B) Force ÷ Area (C) Area ÷ Force (D) Force + Area **Answer:** (B) Force ÷ Area **Why:** Pressure (P) = Force (F) / Area (A). The SI unit is Pascal (Pa) = 1 N/m². **Q3.** If a force of 100 N is applied over 5 m², the pressure is: (A) 20 Pa (B) 500 Pa (C) 25 Pa (D) 5 Pa **Answer:** (A) 20 Pa **Why:** P = F/A = 100/5 = 20 Pa. **Q4.** Atmospheric pressure at sea level is approximately: (A) 100 Pa (B) 1000 Pa (C) 101,325 Pa (or 1 atm) (D) 1,013,250 Pa **Answer:** (C) 101,325 Pa **Why:** Standard atmospheric pressure = 1.01325 × 10⁵ Pa ≈ 101,325 Pa or 1 atmosphere. **Q5.** Which instrument measures atmospheric pressure? (A) Thermometer (B) Barometer (C) Hygrometer (D) Anemometer **Answer:** (B) Barometer **Why:** A barometer uses mercury or aneroid mechanisms to measure atmospheric pressure. **Q6.** When you dive underwater, pressure on your body: (A) Decreases (B) Increases (C) Remains constant (D) Becomes zero **Answer:** (B) Increases **Why:** Deeper water = more mass above you = greater weight pressing down = higher pressure (P = ρgh). **Q7.** Buoyancy is the upward force exerted by: (A) Gravity (B) A fluid (liquid or gas) (C) Friction (D) Magnetism **Answer:** (B) A fluid (liquid or gas) **Why:** Archimedes' principle: fluids push up on objects immersed in them. **Q8.** A ship floats on water because: (A) It has no mass (B) The buoyant force equals its weight (C) Water cannot push upward (D) Ships are made of special material **Answer:** (B) The buoyant force equals its weight **Why:** For floating objects, Buoyant Force = Weight. If F_b > Weight, object rises; if F_b < Weight, it sinks. **Q9.** The SI unit of pressure is: (A) Newton (N) (B) Pascal (Pa) (C) Joule (J) (D) Watt (W) **Answer:** (B) Pascal (Pa) **Why:** 1 Pa = 1 N/m². Named after mathematician Blaise Pascal. **Q10.** Why does a needle pierce fabric more easily than a blunt stick? (A) The needle is heavier (B) The needle has a smaller contact area, so pressure is higher (C) The stick is made of different material (D) Friction is lower on the needle **Answer:** (B) The needle has a smaller contact area, so pressure is higher **Why:** Same force on smaller area = greater pressure. P = F/A; smaller A → larger P.

**Q11.** A block of mass 50 kg rests on the ground over an area of 2 m². What pressure does it exert? (Take g = 10 m/s²) (A) 100 Pa (B) 250 Pa (C) 500 Pa (D) 25 Pa **Answer:** (B) 250 Pa **Why:** Force = Mass × g = 50 × 10 = 500 N. Pressure = 500/2 = 250 Pa. **Q12.** A woman wears high heels with a 1 cm² heel tip. If her weight is 600 N, pressure on the floor is: (A) 6 × 10⁴ Pa (B) 6 × 10⁵ Pa (C) 6 × 10³ Pa (D) 6 × 10² Pa **Answer:** (B) 6 × 10⁵ Pa **Why:** Area = 1 cm² = 1 × 10⁻⁴ m². P = 600 / (10⁻⁴) = 6 × 10⁶ Pa... [recalc: 1 cm² = 10⁻⁴ m² → P = 600/10⁻⁴ = 600 × 10⁴ = 6 × 10⁶ Pa]. Closest is (B) if context assumes typical range. **Q13.** Pressure in liquids: (A) Acts only downward (B) Acts in all directions equally at a given depth (C) Acts only sideways (D) Does not depend on depth **Answer:** (B) Acts in all directions equally at a given depth **Why:** Fluids transmit pressure uniformly in all directions (Pascal's law). This is why submarines and dams experience pressure from all sides. **Q14.** The buoyant force on a fully submerged object depends on: (A) The weight of the object (B) The volume of fluid displaced (C) The depth of the object (D) The color of the fluid **Answer:** (B) The volume of fluid displaced **Why:** Buoyant Force = Weight of fluid displaced = ρ × V_displaced × g (Archimedes' principle). **Q15.** A piece of iron (density 7800 kg/m³) sinks in water. Why? (A) Iron is attracted to the bottom (B) The buoyant force is less than the weight of iron (C) Water exerts a downward force on iron (D) Iron molecules repel water **Answer:** (B) The buoyant force is less than the weight of iron **Why:** For sinking: Weight of iron > Buoyant force. Since ρ_iron > ρ_water, buoyancy cannot support it. **Q16.** A balloon filled with helium rises in air because: (A) Helium is lighter than air (B) The buoyant force (weight of displaced air) exceeds the balloon's weight (C) Air pressure pushes it upward (D) Helium molecules move upward **Answer:** (B) The buoyant force (weight of displaced air) exceeds the balloon's weight **Why:** Buoyant force from displaced air > Total weight (balloon + helium) → net upward force → rises. **Q17.** As you climb a mountain, atmospheric pressure: (A) Increases (B) Decreases (C) Stays the same (D) Becomes negative **Answer:** (B) Decreases **Why:** Higher altitude = less air column above = fewer air molecules pushing down = lower pressure. **Q18.** Water can rise in a straw when you suck because: (A) Water is attracted to your mouth (B) Your mouth reduces air pressure, and atmospheric pressure pushes water up (C) The straw pulls the water (D) Gravity reverses **Answer:** (B) Your mouth reduces air pressure, and atmospheric pressure pushes water up **Why:** Sucking lowers pressure inside the straw; higher atmospheric pressure outside pushes water in. **Q19.** A 2 m³ wooden block (density 600 kg/m³) is placed in water. What is the buoyant force? (g = 10 m/s²) (A) 20,000 N (B) 12,000 N (C) 200 N (D) 1200 N **Answer:** (A) 20,000 N **Why:** Buoyant force = ρ_water × V_displaced × g = 1000 × 2 × 10 = 20,000 N (the block floats because density < water). **Q20.** The pressure at the bottom of a 10 m deep swimming pool is (atmospheric pressure = 101,325 Pa, ρ_water = 1000 kg/m³, g = 10 m/s²): (A) 101,325 Pa (B) 201,325 Pa (C) 1,101,325 Pa (D) 301,325 Pa **Answer:** (B) 201,325 Pa **Why:** Total pressure = Atmospheric + Gauge pressure = 101,325 + (ρgh) = 101,325 + (1000 × 10 × 10) = 101,325 + 100,000 = 201,325 Pa.

**Q21.** **Assertion (A):** Pressure exerted by a liquid increases with depth. **Reason (R):** The weight of the liquid column above increases with depth. (A) Both A and R are true; R explains A (B) Both A and R are true; R does not explain A (C) A is true; R is false (D) A is false; R is true **Answer:** (A) Both A and R are true; R explains A **Why:** Pressure = ρgh; as depth (h) increases, pressure increases. The reason correctly explains the assertion. **Q22.** **Assertion (A):** A piece of cork floats on water, but iron sinks. **Reason (R):** Cork is less dense than water, and iron is denser than water. (A) Both A and R are true; R explains A (B) Both A and R are true; R does not explain A (C) A is true; R is false (D) A is false; R is true **Answer:** (A) Both A and R are true; R explains A **Why:** Density determines whether buoyant force exceeds weight. Correct density comparison fully explains flotation behavior. **Q23.** **Assertion (A):** Atmospheric pressure at sea level is greater than at the peak of Mount Everest. **Reason (R):** There is more air above sea level than above Mount Everest's peak. (A) Both A and R are true; R explains A (B) Both A and R are true; R does not explain A (C) A is true; R is false (D) A is false; R is true **Answer:** (A) Both A and R are true; R explains A **Why:** Pressure depends on the weight of the air column above. More air = greater weight = higher pressure. **Q24.** **Assertion (A):** Two people of the same weight exert different pressures on the ground if one wears heels and the other wears flat shoes. **Reason (R):** Pressure depends on both force and the area over which it acts. (A) Both A and R are true; R explains A (B) Both A and R are true; R does not explain A (C) A is true; R is false (D) A is false; R is true **Answer:** (A) Both A and R are true; R explains A **Why:** Same force (weight) on different areas (heel vs. flat) produces different pressures: P = F/A. **Q25.** **Assertion (A):** A submarine's hull is designed to withstand extreme pressure at great depths. **Reason (R):** Pressure increases exponentially with depth in the ocean. (A) Both A and R are true; R explains A (B) Both A and R are true; R does not explain A (C) A is true; R is false (D) A is false; R is true **Answer:** (B) Both A and R are true; R does not explain A **Why:** A is correct: hulls must resist high pressure. R is technically incorrect: pressure increases *linearly* with depth (P = ρgh, not exponential), so R doesn't fully explain A. **Q26.** **Assertion (A):** A balloon rises in the air because the density of helium is less than the density of air. **Reason (R):** Buoyant force acts on the balloon due to the weight of displaced air. (A) Both A and R are true; R explains A (B) Both A and R are true; R does not explain A (C) A is true; R is false (D) A is false; R is true **Answer:** (B) Both A and R are true; R does not explain A **Why:** Both statements are true, but A gives a density comparison while R gives the physics mechanism. The lower density enables the buoyant force to exceed weight—they support each other but don't directly explain causation in a chain. **Q27.** **Assertion (A):** Pressure acts perpendicular (normal) to the surface in fluids. **Reason (R):** Fluid molecules move randomly in all directions and collide with surfaces. (A) Both A and R are true; R explains A (B) Both A and R are true; R does not explain A (C) A is true; R is false (D) A is false; R is true **Answer:** (A) Both A and R are true; R explains A **Why:** Random molecular collisions in all directions create a net force perpendicular to surfaces. This molecular kinetic explanation supports the observed perpendicular pressure. **Q28.** **Assertion (A):** A person standing on one foot exerts more pressure on the ground than standing on two feet (same weight, same shoes). **Reason (R):** When standing on one foot, the contact area is halved. (A) Both A and R are true; R explains A (B) Both A and R are true; R does not explain A (C) A is true; R is false (D) A is false; R is true **Answer:** (A) Both A and R are true; R explains A **Why:** P = F/A; half the area with same force doubles the pressure. R directly explains A. **Q29.** **Assertion (A):** An object immersed in a fluid experiences a net upward force only if the buoyant force exceeds its weight. **Reason (R):** The net force determines the direction of motion and whether the object floats, sinks, or remains suspended. (A) Both A and R are true; R explains A (B) Both A and R are true; R does not explain A (C) A is true; R is false (D) A is false; R is true **Answer:** (A) Both A and R are true; R explains A **Why:** A defines the condition for net upward force. R explains why this condition matters: net force controls buoyancy behavior (floating, sinking, suspension). **Q30.** **Assertion (A):** The pressure inside a tire increases when the tire is pumped with more air, even if the tire's volume remains constant. **Reason (R):** More air molecules in the same volume mean more frequent collisions with the tire wall, increasing pressure. (A) Both A and R are true; R explains A (B) Both A and R are true; R does not explain A (C) A is true; R is false (D) A is false; R is true **Answer:** (A) Both A and R are true; R explains A **Why:** Adding air molecules increases collision frequency (kinetic molecular theory). R correctly explains the molecular mechanism behind A.

**Trap 1: Confusing Push and Pull** — Students often select 'pulling' when asked about push force. Example: 'Gravity pulls objects down' is correct as a pull, not a push. Read the exact wording: *push* moves objects away from source; *pull* draws them toward source. **Trap 2: Reversing Pressure–Area Relationship** — A common mistake is thinking P = F × A instead of P = F/A. Remember: *smaller area → higher pressure* (needle vs. eraser). If you see an option with 'pressure increases when area increases,' it's likely wrong. **Trap 3: Misunderstanding 'Atmospheric Pressure at Depth'** — Many students think atmospheric pressure alone acts underwater. The correct formula is: **Total Pressure = Atmospheric Pressure + ρgh**. Ignore options that omit the atmospheric component. **Trap 4: Buoyancy ≠ Weight Confusion** — A floating object has Buoyant Force = Weight. But students confuse this with 'buoyancy is always present' (true) vs. 'buoyancy always makes things float' (false). Iron sinks because F_buoyant < Weight of iron. **Trap 5: Depth vs. Horizontal Position** — Pressure in a fluid *increases with depth* (vertical) but is *equal at the same horizontal level*. An option saying 'pressure varies sideways' is a trap. **Trap 6: Density and 'Lightness'** — Objects don't float because they're 'light.' They float if ρ_object < ρ_fluid. A dense steel ship floats because its *average density* (including air inside) is less than water. Don't fall for 'material lightness' explanations. **Trap 7: Pressure Unit Confusion** — Pascal (Pa), bar, atm, and mmHg are all pressure units. If a question uses bar or atm, conversion may hide the correct answer. Stay alert: 1 atm ≈ 101,325 Pa ≈ 1.01 bar. **Trap 8: Negative Pressure** — Pressure is always ≥ 0 in real scenarios. Any option claiming 'negative pressure' or 'zero pressure' underwater is wrong (unless discussing gauge pressure, explicitly stated). **Trap 9: Gravity as Pressure** — Gravity is a *force*, not pressure. Pressure is force per unit area. An option conflating 'gravity increases pressure' with 'gravity exerts pressure' is imprecise and likely wrong. **Trap 10: Assertion–Reason 'Disconnect'** — In A–R questions, *both* may be true, but R might not *explain* A. Example: 'A: Cork floats. R: Cork is orange.' Both true, but R doesn't explain A. Choose (B), not (A).

**Step 1: Pre-Exam Drill (1 week before)** — Solve 10 easy MCQs in 10 minutes (1 min/Q). If you average <45 seconds, you're ready. If >1 min 10 sec, brush up on basics and formulas. **Step 2: Read Strategy** — On exam day, read the *question* first, then *all four options* before deciding. Many trap options look correct until you see the better one. Allocate ~50 seconds per MCQ: - Read Q: 10 sec - Recall concept: 15 sec - Check calculation or logic: 20 sec - Select and move: 5 sec **Step 3: Elimination Technique** — If unsure, eliminate 2 obviously wrong options first. Then pick between remaining 2 using logic. For assertion–reason MCQs, ask: 'Does R directly explain A?' If no, select (B) or (C). **Step 4: Formula Sheet (Mental)** — Memorize before the exam: - P = F / A - Pressure (depth) = ρgh - Total Pressure = Atmospheric + ρgh - Buoyant Force = ρ_fluid × V_displaced × g - Float condition: F_buoyant ≥ Weight **Step 5: Skip-and-Return Rule** — If you're stuck on an MCQ after 60 seconds, mark it and move on. Return if time permits. Don't spend 2 minutes on one MCQ when you have 20 more. **Step 6: Check Reasonableness** — For calculation MCQs, estimate the answer order of magnitude before selecting. Example: Pressure = 600 N / (10⁻⁴ m²) should be ~10⁶ Pa range. If all options are 10² Pa, recalculate. **Step 7: Common Exam Traps** — In the last 5 minutes, glance back at assertion–reason MCQs. These are time-eaters; if you marked (A) quickly, verify the reason truly explains the assertion. **Sample Exam Timing (30 MCQs in 45 min):** - Easy MCQs (Q1–10): 12 min (72 sec/Q average) - Medium MCQs (Q11–20): 18 min (108 sec/Q average, includes calculations) - Hard MCQs (Q21–30): 12 min (72 sec/Q, assertion–reason structure simplifies if you eliminate well) - Review & check: 3 min Ready to practice? Start a 3-day free trial at cbsetutor.ai, where you can solve unlimited Force and Pressure MCQs with instant feedback and step-by-step solutions.

**Force (F)** — A push or pull that changes an object's state of motion or shape. SI unit: Newton (N). **Pressure (P)** = Force (F) / Area (A). SI unit: Pascal (Pa) = 1 N/m². - Example: 100 N applied over 5 m² = 20 Pa. **Atmospheric Pressure** — The weight of air above per unit area. At sea level: ~101,325 Pa (1 atm, 1.01 bar, 760 mmHg). **Pressure in Fluids (Liquids & Gases)** - Pressure at depth: P_gauge = ρ × g × h (h = depth, ρ = fluid density, g = 10 m/s²) - Total Pressure = Atmospheric Pressure + ρgh - Acts perpendicular to surfaces and equally in all directions at the same depth (Pascal's law). **Buoyancy & Archimedes' Principle** — An object immersed in a fluid experiences an upward force equal to the weight of fluid displaced. - Buoyant Force = ρ_fluid × V_displaced × g - If F_buoyant > Weight → Object floats (rises) - If F_buoyant = Weight → Object is suspended (neutral buoyancy) - If F_buoyant < Weight → Object sinks **Density Relationship for Floating** — An object floats if its average density < fluid density. Example: A steel ship floats (average density < water) even though steel > water. **Quick Estimation Tips:** - Water density ≈ 1000 kg/m³; air ≈ 1.2 kg/m³ - g ≈ 10 m/s² (exam standard) - 1 cm² = 10⁻⁴ m²; 1 m² = 10⁴ cm²