General Q&A for Class 12 · Page 178
5,215 free answers in General for Class 12 students, across CBSE, ICSE and State boards.
Question & Answer
Questions
- GeneralClass 12All
What is F = -kx?
This is Hooke's Law for elastic springs: F = restoring force (N) k = spring constant (N/m) x = displacement from equilibrium (m) Negative sign indicates force opposes displacement Work done to stretch/compress a spring: W = ½kx²
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How to use F = -kx?
To apply Hooke's Law: Identify spring constant (k) - measure of stiffness Measure displacement (x) from natural length Calculate force: F = kx (magnitude) Note direction: Force always opposes displacement Example: A spring with k = 200 N/m stretched 0.1m: F = 200 × 0.1 = 20N (opposing the stretch)
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What is f delta t?
F × Δt represents impulse, the change in momentum: F = average force (N) Δt = time interval (s) Impulse = change in momentum = Δp = mΔv This is from the impulse-momentum theorem: F × Δt = m(v_f - v_i) Different from work (F × d), impulse involves force over time rather than distance.
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What do v, λ, and f stand for?
In wave physics: v = wave velocity or speed (m/s) λ (lambda) = wavelength (m) f = frequency (Hz or cycles/second) Relationship: v = f × λ This fundamental wave equation connects speed, frequency, and wavelength for all waves.
- GeneralClass 12All
What is δθ in physics?
δθ (delta theta) typically represents: Small angular displacement (radians or degrees) Infinitesimal change in angle Used in rotational motion, torque, and angular work calculations Related formula: Work in rotation = τ × δθ The lowercase δ indicates an infinitesimal or very small change.
- GeneralClass 12All
In fluid mechanics/thermodynamics (pressure):
Δp = P_final - P_initial Unit: Pascal (Pa) or atmospheres
- GeneralClass 12All
What does Δp mean?
Δp (delta p) indicates change in a quantity starting with "p": Momentum: Δp = impulse = F × Δt Pressure: Δp used in Bernoulli's equation, pressure drop calculations The Greek letter Δ (delta) universally means "change in" or "difference"
- GeneralClass 12All
In mechanics (momentum):
Δp = p_final - p_initial = m(v_f - v_i) Unit: kg·m/s
- GeneralClass 12All
What is Δp Δt?
Δp/Δt equals average force according to Newton's second law: Δp = change in momentum (kg·m/s) Δt = time interval (s) F_avg = Δp/Δt This represents how quickly momentum changes. Alternative form: F = dp/dt (instantaneous force as rate of momentum change).
- GeneralClass 12All
What is Δt?
Δt (delta t) represents change in time or time interval: Δt = t_final - t_initial Measured in seconds, minutes, or hours Used in formulas for velocity (v = Δd/Δt), acceleration (a = Δv/Δt), power (P = W/Δt)
- GeneralClass 12All
What is Δp?
Δp represents change in momentum or change in pressure depending on context:
- GeneralClass 12All
What is delta G = -nFE?
This is the Gibbs free energy formula for electrochemical reactions: ΔG = change in Gibbs free energy (J or kJ) n = number of moles of electrons transferred F = Faraday's constant (96,485 C/mol) E = cell potential (volts) Relates electrical work to free energy change in redox reactions. Negative ΔG indicates spontaneous reaction.
- GeneralClass 12All
How to use the formula q = mcΔt?
To use this heat transfer formula: Identify the mass (m) of the substance Find specific heat capacity (c) from tables Calculate temperature change: Δt = t_final - t_initial Multiply: q = m × c × Δt Example: Heat 100g of water from 20°C to 80°C (c = 4.18 J/g°C): q = 100 × 4.18 × (80-20) = 25,080 J
- GeneralClass 12All
What formula is q = mcΔt?
This is the heat transfer formula: q = heat energy transferred (joules) m = mass of substance (kg or g) c = specific heat capacity (J/kg·K or J/g·°C) Δt = temperature change (K or °C) This calculates energy required to change a substance's temperature. Not directly work, but related through the first law of thermodynamics.
- GeneralClass 12All
How to calculate W in physics?
Calculating work (W) in physics: Identify all forces acting on the object Measure displacement in the direction of motion Determine the angle between force and displacement Apply formula: W = F × d × cos(θ) Consider sign: Positive if force aids motion, negative if opposes For variable forces, use integration: W = ∫F(x
- GeneralClass 12All
How to calculate total work?
To calculate total work when multiple forces act: Method 1: Find net force (ΣF), then W_total = F_net × d × cos(θ) Method 2: Calculate work by each force separately, then sum: W_total = W₁ + W₂ + W₃ + ... Method 3: Use Work-Energy Theorem: W_total = ΔKE Example: If gravity does -50J and applied force does +80J, total work = 30J.
- GeneralClass 12All
What are the three ways to calculate work?
Three primary methods to calculate work: Direct formula: W = F × d × cos(θ) - for constant force Work-Energy Theorem: W = ΔKE = ½m(v₂² - v₁²) Integration: W = ∫F·ds - for variable force Each method suits different scenarios: constant vs. variable force, known velocities vs. known forces.
- GeneralClass 12All
How do you calculate total displacement?
To calculate total displacement: For straight-line motion: Subtract the initial position from the final position For motion in multiple directions: Use vector addition. Break each displacement into components (x and y directions), add all x-components together and all y-components together, then use the Pythagorean theorem: Total displacement = √(Δx² + Δy²) From a velocity
- GeneralClass 12All
How do you calculate displacement from a velocity-time graph?
The displacement from a velocity-time (v-t) graph equals the area under the curve. For a straight horizontal line (constant velocity), the area is a rectangle: displacement = velocity × time. For uniformly accelerated motion (sloped line), the area forms a trapezoid or triangle. Remember that areas above the time axis represent positive displacement, while areas below represent negative displacement (motion in the opposite direction).
- GeneralClass 12All
What is the equation of motion for displacement?
There are three primary equations of motion for displacement: v = u + at (relates velocity, initial velocity, acceleration, and time) s = ut + ½at² (gives displacement directly) v² = u² + 2as (connects velocities, acceleration, and displacement without time) These equations apply only when acceleration is constant. They're fundamental tools for solving kinematics problem