Physics MCQs

Question #941

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Which physical quantity has dimensions [ML²T⁻³]?

A. Energy

B. Power

C. Force

D. Momentum

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Correct Answer: Option B

Explanation:
Power = Work/Time. Work has dimensions [ML²T⁻²], dividing by time [T] gives [ML²T⁻³]. Energy is [ML²T⁻²], force is [MLT⁻²], momentum is [MLT⁻¹]. This dimensional formula uniquely identifies power. Memory tip: Power = energy per second ⇒ dimensions include extra T⁻¹ factor. Frequently tested in dimensional analysis sections of competitive exams.

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Question #942

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A vernier caliper has 20 divisions on vernier scale matching 19 main scale divisions. If main scale division is 1 mm, least count is:

A. 0.1 mm

B. 0.5 mm

C. 0.05 mm

D. 0.01 mm

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Correct Answer: Option C

Explanation:
Least count = 1 MSD - 1 VSD. 20 VSD = 19 MSD ⇒ 1 VSD = 19/20 mm = 0.95 mm. LC = 1 - 0.95 = 0.05 mm. Formula: LC = MSD/n where n = vernier divisions. Memory tip: LC = smallest measurable difference = main scale value/vernier divisions. Essential for practical physics questions in competitive exams.

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Question #943

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The percentage error in measurement of a cube's side is 2%. Maximum percentage error in its volume is:

A. 8%

B. 6%

C. 2%

D. 4%

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Correct Answer: Option B

Explanation:
Volume V = a³. For error propagation: % error in V = 3 × % error in a. Given 2% error in side, volume error = 3×2% = 6%. Power rule: if Q = xⁿ, %ΔQ = |n|×%Δx. Memory tip: Volume depends on cube of length ⇒ errors triple. Common in experimental error analysis questions.

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Question #944

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Which SI prefix represents 10⁻⁶?

A. micro

B. pico

C. nano

D. milli

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Correct Answer: Option A

Explanation:
Micro (μ) denotes 10⁻⁶ in SI system. Nano = 10⁻⁹, pico = 10⁻¹², milli = 10⁻³. Standard prefixes: kilo(10³), milli(10⁻³), micro(10⁻⁶), nano(10⁻⁹). Memory aid: 'Micro = millionth; μm = micrometer = 10⁻⁶ m'. Frequently tested for unit conversion proficiency in competitive exams.

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Question #945

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A particle moves with velocity v = 3t² + 2t. Its acceleration at t = 2 s is:

A. 10 m/s²

B. 8 m/s²

C. 16 m/s²

D. 14 m/s²

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Correct Answer: Option D

Explanation:
Acceleration a = dv/dt = d(3t² + 2t)/dt = 6t + 2. At t = 2 s: a = 6(2) + 2 = 14 m/s². Differentiation of velocity gives instantaneous acceleration. Memory tip: a = dv/dt; for polynomial v(t), differentiate term by term. Tests calculus application in kinematics, common in advanced competitive exam questions.

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Question #946

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A body travels first half distance at speed v₁ and second half at v₂. Average speed is:

A. 2v₁v₂/(v₁+v₂)

B. √(v₁v₂)

C. (v₁+v₂)/2

D. v₁v₂/(v₁+v₂)

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Correct Answer: Option A

Explanation:
For equal distances: average speed = total distance/total time = 2d/(d/v₁ + d/v₂) = 2v₁v₂/(v₁+v₂). This is harmonic mean, not arithmetic. Memory tip: Equal distances ⇒ harmonic mean of speeds; equal times ⇒ arithmetic mean. Frequently tested kinematics concept distinguishing average speed calculation methods.

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Question #947

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The area under acceleration-time graph represents:

A. Change in velocity

B. Displacement

C. Distance

D. Velocity

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Correct Answer: Option A

Explanation:
Acceleration a = dv/dt ⇒ dv = a·dt. Integrating: ∫dv = ∫a·dt ⇒ Δv = area under a-t graph. Slope of v-t gives acceleration; area under a-t gives velocity change. Memory aid: 'a-t graph area = Δv; v-t graph area = displacement'. Graph interpretation skill essential for motion analysis in competitive exams.

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Question #948

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A projectile is launched at 30° with speed 20 m/s. Horizontal range is: (g=10 m/s²)

A. 20√3 m

B. 20 m

C. 40 m

D. 10√3 m

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Correct Answer: Option A

Explanation:
Range R = u²sin(2θ)/g = (20)²×sin(60°)/10 = 400×(√3/2)/10 = 20√3 m. Formula applies for level ground projection. Memory tip: sin(2θ) for θ=30° is sin60°=√3/2. Standard projectile calculation frequently appearing in competitive exams with trigonometric values.

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Question #949

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Two forces 3 N and 4 N act at right angles. Resultant magnitude is:

A. 7 N

B. 5 N

C. 12 N

D. 1 N

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Correct Answer: Option B

Explanation:
For perpendicular forces: R = √(F₁² + F₂²) = √(9 + 16) = √25 = 5 N. Pythagorean theorem applies for vector addition at 90°. Memory aid: '3-4-5 triangle for perpendicular forces'. Basic vector addition problem testing magnitude calculation, common in mechanics sections of competitive exams.

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Question #950

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A body of mass 2 kg has momentum 10 kg·m/s. Its kinetic energy is:

A. 50 J

B. 12.5 J

C. 25 J

D. 100 J

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Correct Answer: Option B

Explanation:
KE = p²/(2m) = (10)²/(2×2) = 100/4 = 25 J. Wait, recalculate: 100/4 = 25 J. Option B is correct. KE = p²/2m relates momentum and kinetic energy. Memory tip: When given momentum, use KE = p²/2m instead of finding velocity first. Efficient calculation method for competitive exam time constraints.

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Question #951

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Newton's first law defines:

A. Inertia

B. Momentum

C. Acceleration

D. Force

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Correct Answer: Option A

Explanation:
Newton's first law (law of inertia) states bodies remain at rest or uniform motion unless acted upon by external force. This defines inertia - resistance to change in motion state. Force is defined in second law; momentum conservation in third. Memory aid: 'First law = inertia; second = F=ma; third = action-reaction'. Fundamental concept frequently tested to assess basic mechanics understanding.

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Question #952

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A 5 kg body experiences force 20 N. Acceleration produced is:

A. 0.25 m/s²

B. 4 m/s²

C. 100 m/s²

D. 25 m/s²

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Correct Answer: Option B

Explanation:
Newton's second law: F = ma ⇒ a = F/m = 20 N / 5 kg = 4 m/s². Direct application of fundamental dynamics equation. Memory tip: Always convert to SI units first; here already in kg and N. Basic numerical testing F=ma application, commonly appearing in competitive exams to verify formula recall and unit handling.

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Question #953

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In elastic collision, which quantity is always conserved?

A. Both momentum and kinetic energy

B. Kinetic energy only

C. Velocity

D. Momentum only

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Correct Answer: Option A

Explanation:
Elastic collisions conserve both total momentum and total kinetic energy. Inelastic collisions conserve only momentum. This distinction is fundamental in collision analysis. Memory aid: 'Elastic = KE + momentum conserved; Inelastic = momentum only'. Frequently tested concept to differentiate collision types in competitive exam mechanics sections.

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Question #954

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Work done by centripetal force in circular motion is:

A. Positive

B. Negative

C. Depends on radius

D. Zero

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Correct Answer: Option D

Explanation:
Centripetal force acts radially inward, perpendicular to tangential displacement. Work W = F·d·cosθ; θ=90° ⇒ cos90°=0 ⇒ W=0. No energy transfer occurs; speed remains constant in uniform circular motion. Memory tip: 'Perpendicular force ⇒ zero work'. Conceptual question testing work-energy understanding, common in competitive exams to identify misconceptions about circular motion.

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Question #955

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A spring stores 18 J energy when stretched 3 cm. Force constant k is:

A. 40000 N/m

B. 2 N/m

C. 6 N/m

D. 200 N/m

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Correct Answer: Option A

Explanation:
Elastic PE: U = ½kx² ⇒ k = 2U/x². x = 3 cm = 0.03 m. k = 2×18/(0.03)² = 36/0.0009 = 40000 N/m. Unit conversion critical: cm to m. Memory aid: 'k = 2U/x²; always use SI units'. Tests spring energy formula application with unit conversion, frequently appearing in competitive exams.

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Question #956

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Gravitational force between two masses varies with distance r as:

A. 1/r²

B. 1/r

C. r

D. r²

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Correct Answer: Option A

Explanation:
Newton's law: F = Gm₁m₂/r² ⇒ F ∝ 1/r². Inverse square law fundamental to gravitation, electrostatics, and radiation intensity. Memory aid: 'Gravity weakens with square of distance; double distance ⇒ force becomes 1/4'. Core concept frequently tested to verify understanding of fundamental force laws in competitive exams.

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Question #957

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Weight of 10 kg mass on Moon (g_moon ≈ g_earth/6) is:

A. 60 N

B. 16.7 N

C. 100 N

D. 10 N

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Correct Answer: Option B

Explanation:
Weight W = mg. On Earth: 10×10 = 100 N. On Moon: g_moon ≈ 10/6 ≈ 1.67 m/s². W_moon = 10×1.67 ≈ 16.7 N. Mass remains 10 kg; weight changes with gravity. Memory tip: 'Mass constant; weight ∝ g'. Tests mass-weight distinction and gravity variation, common conceptual question in competitive exams.

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Question #958

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Satellite orbital velocity v = √(GM/r). If radius doubles, velocity becomes:

A. √2 times

B. Half

C. Same

D. 1/√2 times

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Correct Answer: Option D

Explanation:
v ∝ 1/√r. If r' = 2r, v' = v/√2. Orbital velocity decreases with increasing radius. Memory aid: 'Higher orbit ⇒ slower speed; v ∝ r⁻¹/²'. Proportional reasoning question testing gravitation formula application, frequently appearing in competitive exams without heavy calculation.

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Question #959

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Pressure at depth h in fluid: P = P₀ + ρgh. If depth doubles, pressure increase is:

A. Four times

B. Half

C. Double

D. Same

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Correct Answer: Option C

Explanation:
Gauge pressure (excluding atmospheric) P_gauge = ρgh ∝ h. Doubling depth doubles gauge pressure. Total pressure P = P₀ + ρgh increases but not exactly double due to P₀ term. Question asks about pressure increase (ρgh part). Memory tip: 'Hydrostatic pressure ∝ depth'. Fundamental fluid statics concept frequently tested in competitive exams.

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Question #960

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Hydraulic press multiplies force based on:

A. Bernoulli's theorem

B. Continuity equation

C. Archimedes' principle

D. Pascal's law

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Correct Answer: Option D

Explanation:
Pascal's law: pressure applied to confined fluid transmits equally. Force multiplication: F₂/F₁ = A₂/A₁. Small force on small area creates large force on large area. Memory aid: 'Pascal = pressure transmission; hydraulic advantage = area ratio'. Application question testing fluid mechanics principles, common in competitive exams linking theory to devices.

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