General Q&A for Class 12 · Page 179
5,215 free answers in General for Class 12 students, across CBSE, ICSE and State boards.
Question & Answer
Questions
- GeneralClass 12All
What is resultant displacement?
Resultant displacement is the single displacement that has the same effect as two or more individual displacements combined. When an object undergoes multiple displacements, you find the resultant by vector addition. For example, if you walk 3 meters north and then 4 meters east, your resultant displacement is 5 meters in a northeast direction (calculated using the Pythagorean theorem: √(3² + 4²) = 5 meters).
- GeneralClass 12All
Is displacement represented by Δd or Δs?
Displacement is commonly represented by Δs (delta s) in many physics textbooks, though Δd (delta d) is also used in some contexts. The Greek letter delta (Δ) means "change in," so both notations indicate a change in position. The symbol s is traditional for displacement in equations of motion, while d might be used when emphasizing the directional aspect or in vector notation.
- GeneralClass 12All
How do you find displacement in kilometers?
To find displacement in kilometers, use the same displacement formulas but ensure all units are consistent. If you calculate displacement in meters, divide by 1,000 to convert to kilometers. For example, if displacement = 5,000 meters, then displacement = 5 km. When using formulas like s = ut + ½at², make sure velocity is in km/h or convert it appropriately, and time matches the velocity units.
- GeneralClass 12All
What is final displacement?
Final displacement refers to an object's position relative to its starting point at the end of its motion. It's the net change in position after all movements are complete. In problems involving multiple stages of motion, the final displacement is the vector sum of all individual displacements. If an object returns to its starting point, the final displacement is zero, regardless of the path taken.
- GeneralClass 12All
What is a displacement reaction in chemistry?
A displacement reaction (also called a substitution reaction) occurs when a more reactive element displaces a less reactive element from its compound. For example, when zinc is added to copper sulfate solution, zinc displaces copper: Zn + CuSO₄ → ZnSO₄ + Cu. The rule is that a more reactive metal displaces a less reactive metal from its salt solution. This is different from physical displacement but uses the same concept of "replacing" or "taking the position of" somethi
- GeneralClass 12All
How do you calculate displacement graphically?
On a position-time graph, displacement is the vertical distance between two points on the curve. On a velocity-time graph, displacement is the area between the curve and the time axis. For complex motion, break the graph into simpler shapes (rectangles, triangles, trapezoids), calculate each area separately, and add them together with appropriate signs (positive for forward motion, negative for backward motion).
- GeneralClass 12All
How do you solve distance and displacement problems?
Follow these steps: Identify the motion type: Is it straight-line or two-dimensional? Constant velocity or acceleration? Note initial and final positions: Mark the starting point and ending point For distance: Add up all path segments traveled For displacement: Find the straight-line distance and direction from start to finish Use appropriate formulas: Ap
- GeneralClass 12All
What is displacement current?
Displacement current is a concept in electromagnetism introduced by James Clerk Maxwell. It's not actually a flow of charge like conventional current, but rather a term that accounts for the changing electric field in regions where no actual current flows (like between capacitor plates). The formula is I_d = ε₀(dΦ_E/dt), where ε₀ is the permittivity of free space and dΦ_E/dt is the rate of change of electric flux. This concept is typically covered in a
- GeneralClass 12All
What is the formula for terminal velocity?
Terminal velocity is: v_t = √(2mg/ρAC_d) where m is mass, g is gravity, ρ (rho) is air density, A is cross-sectional area, and C_d is the drag coefficient. Why area matters: Larger area = more air resistance = lower terminal velocity This is why skydivers spread out to slow down and tuck in to speed up Terminal velocity for humans: ~53 m/s (190 km/h) belly-down, ~90 m/s (320 km/h) head-down
- GeneralClass 12All
What is the formula for calculating the velocity of a satellite?
For a satellite in circular orbit: v = √(GM/r) where G is gravitational constant, M is Earth's mass, and r is the distance from Earth's center (radius of Earth + altitude). For low Earth orbit (~400 km altitude): Orbital velocity ≈ 7.7 km/s or 27,720 km/h Completes one orbit in about 90 minutes
- GeneralClass 12All
How do you convert angular velocity to linear velocity?
Use the formula: v = rω where v is linear velocity, r is the radius from the rotation axis, and ω (omega) is angular velocity in radians per second. Key conversions: If angular velocity is in RPM: ω (rad/s) = RPM × 2π / 60 If angular velocity is in degrees/s: ω (rad/s) = degrees/s × π / 180 Points farther from the axis move fa
- GeneralClass 12All
What is the formula for finding the velocity of water?
For fluid flow through pipes or channels, use the continuity equation: v = Q/A where Q is volumetric flow rate and A is cross-sectional area. For water exiting from a tank at height h (Torricelli's theorem): v = √(2gh) Example: Water in a tank 5 meters above the outlet exits at v = √(2 × 9.8 × 5) = √98 ≈ 9.9 m/s.
- GeneralClass 12All
What is the formula for relative velocity?
Relative velocity of A with respect to B is: v_AB = v_A - v_B (vector subtraction). This tells you how fast and in what direction A appears to move from B's perspective. Important cases: Same direction: subtract speeds (60 km/h - 40 km/h = 20 km/h) Opposite directions: add speeds (60 km/h - (-40 km/h) = 100 km/h) Perpendicular motion: use Pythagorean theorem √(v
- GeneralClass 12All
How does relativistic velocity addition work
Unlike classical physics, velocities don't simply add at high speeds. The relativistic formula is: v = (v₁ + v₂)/(1 + v₁v₂/c²) where c is the speed of light. Why this matters: Classical: If you throw a ball at 10 m/s from a train moving 20 m/s, ball speed = 30 m/s ✓ Relativistic: If spaceship A moves at 0.9c and fires a projectile at 0.9c, projectile speed ≠ 1.8c
- GeneralClass 12All
Why can't anything travel faster than the speed of light?
According to Einstein's special relativity, as an object approaches the speed of light (c ≈ 299,792,458 m/s), its mass effectively increases, requiring infinite energy to reach light speed. The relativistic mass formula is: m = m₀/√(1 - v²/c²) What happens at high speeds: ● At 90% light speed, mass increases by 2.3 times ● At 99% light speed, mass increases by 7 times ● At 100% light speed, mass would be infinite (impossible) Insight: This is a fundamental law of physics
- GeneralClass 12All
How do I choose the right velocity formula for my problem?
Follow this decision tree based on what you know: Know distance and time? → Use v = d/t Know initial velocity, acceleration, and time? → Use v = u + at Know acceleration and distance (no time)? → Use v² = u² + 2as Know kinetic energy and mass? → Use v = √(2KE/m) Know momentum and mass? → Use v = p/
- GeneralClass 12All
What units should I use for velocity calculations?
Always use consistent SI units for accurate calculations: meters (m) for distance, seconds (s) for time, kilograms (kg) for mass. This gives velocity in m/s. Common conversions: 1 km/h = 0.278 m/s (divide by 3.6) 1 mph = 0.447 m/s (multiply by 0.447) 1 m/s = 3.6 km/h (multiply by 3.6) 1 m/s = 2.237 mph (multiply by 2.237)
- GeneralClass 12All
What's the difference between speed and velocity?
Speed is a scalar (magnitude only) while velocity is a vector (magnitude and direction). Speed = distance/time Velocity = displacement/time Main differences: Speed is always positive; velocity can be negative (indicating opposite direction) Average speed uses total distance; average velocity uses displacement A car going around a circular track has speed but may have zero average velo
- GeneralClass 12All
How do you find velocity without knowing time?
Use formulas that don't include time: v² = u² + 2as (when you know acceleration and distance) v = √(2gh) (for free fall from height) v = √(2KE/m) (from kinetic energy) v = p/m (from momentum) Note: These energy and momentum approaches are particularly useful in collision problems where time is unknown or irrelevant.
- GeneralClass 12All
What is displacement in physics?
Displacement is a vector quantity that represents the shortest straight-line distance between an object's initial position and its final position, along with the direction of that line. Unlike distance, which measures the total path traveled, displacement only considers where you started and where you ended up. For example, if you walk 10 meters east and then 10 meters west, your total distance is 20 meters, but your displacement is zero because you're back at your starting point.