ISC Class 11 Physics Flashcards

24 sample cards from the Physics deck

Sampled from the end of the deck, so these are different cards from the ones shown on the syllabus page.

1. Define impulse and state the impulse-momentum theorem.

   Impulse = force x time = F·Δt (vector). The impulse-momentum theorem states impulse equals the change in momentum: F·Δt = Δp = mv − mu.

2. Distinguish between static, limiting and kinetic friction.

   Static friction is the self-adjusting force opposing impending motion (0 up to a maximum); limiting friction is its maximum value just before sliding; kinetic friction acts once the body is sliding and is generally less than limiting friction.

3. State the laws of limiting friction (relation between friction and normal force).

   Limiting friction f = μ_s N, where μ_s is the coefficient of static friction and N the normal reaction; it is independent of the apparent area of contact and depends on the nature of surfaces.

4. What is the angle of friction, and how is it related to the coefficient of friction?

   The angle of friction λ is the angle between the resultant of friction and normal force and the normal reaction. tanλ = μ (coefficient of friction).

5. Derive the maximum safe speed for a vehicle on a level circular road of radius r.

   Friction provides centripetal force: μmg = mv²/r, so maximum speed v_max = √(μrg).

6. What is banking of roads and why is it done?

   Banking is raising the outer edge of a curved road above the inner edge. It provides a component of the normal reaction to supply the centripetal force, reducing dependence on friction and allowing safer turns.

7. Define work done by a constant force and state when work is zero.

   Work W = F·s = Fs cosθ (force times displacement times cosine of angle between them). Work is zero when force is perpendicular to displacement (θ = 90°) or when displacement is zero.

8. State the work-energy theorem.

   The net work done by all forces on a body equals the change in its kinetic energy: W_net = ΔKE = (1/2)mv² − (1/2)mu².

9. Define kinetic energy and potential energy, giving their formulas.

   Kinetic energy is energy due to motion: KE = (1/2)mv². Potential energy is energy due to position/configuration; gravitational PE near Earth = mgh.

10. State the law of conservation of mechanical energy.

    In the absence of non-conservative forces (like friction), the total mechanical energy (KE + PE) of a system remains constant.

11. Define power and give its SI unit and the relation P = F·v.

    Power is the rate of doing work: P = W/t. SI unit is the watt (W = J/s). Instantaneous power = F·v = Fv cosθ (force times velocity).

12. Differentiate between elastic and inelastic collisions.

    In an elastic collision both momentum and kinetic energy are conserved. In an inelastic collision momentum is conserved but kinetic energy is not (some is lost); in a perfectly inelastic collision the bodies stick together.

13. In a one-dimensional elastic collision between equal masses (one at rest), what happens to their velocities?

    They exchange velocities: the moving body stops and the stationary body moves off with the original velocity of the first.

14. Define the coefficient of restitution.

    e = (relative velocity of separation)/(relative velocity of approach). e = 1 for perfectly elastic, e = 0 for perfectly inelastic, and 0 < e < 1 for real collisions.

15. Define the centre of mass of a system of particles.

    It is the point at which the entire mass of the system may be considered concentrated for describing translational motion; its position is the mass-weighted average of the positions of all particles: R = (Σmᵢrᵢ)/(Σmᵢ).

16. How does the centre of mass of a system move when only internal forces act?

    If the net external force is zero, the centre of mass moves with constant velocity (or stays at rest); internal forces cannot change the motion of the centre of mass.

17. Define torque (moment of force) and write its formula.

    Torque is the turning effect of a force about an axis: τ = r x F, magnitude τ = rF sinθ, where r is the position vector of the point of application and θ the angle between r and F. SI unit: N·m.

18. Define angular momentum and state its relation to torque.

    Angular momentum L = r x p (magnitude rp sinθ). Torque equals the rate of change of angular momentum: τ = dL/dt.

19. State the law of conservation of angular momentum with an everyday example.

    If the net external torque on a system is zero, its total angular momentum remains constant. Example: a spinning ice-skater pulls in arms to reduce moment of inertia and spins faster (L = Iω constant).

20. Define moment of inertia and state the factors it depends on.

    Moment of inertia I = Σmᵢrᵢ² is the rotational analogue of mass, measuring resistance to angular acceleration. It depends on the total mass, its distribution about the axis, and the position/orientation of the axis of rotation.

21. State the theorem of parallel axes.

    The moment of inertia about any axis equals the moment of inertia about a parallel axis through the centre of mass plus Md²: I = I_cm + Md², where d is the distance between the two parallel axes.

22. State Newton's law of universal gravitation.

    Every particle attracts every other particle with a force directly proportional to the product of their masses and inversely proportional to the square of the distance between them: F = G m₁m₂/r².

23. State Kepler's three laws of planetary motion.

    1) Law of orbits: planets move in ellipses with the Sun at one focus. 2) Law of areas: the line joining a planet to the Sun sweeps equal areas in equal times. 3) Law of periods: T² ∝ a³ (square of period proportional to cube of semi-major axis).

24. Write the formulas for the orbital velocity and escape velocity of a satellite near Earth's surface.

    Orbital velocity v_o = √(gR) ≈ 7.9 km/s; Escape velocity v_e = √(2gR) = √(2GM/R) ≈ 11.2 km/s. Thus v_e = √2 × v_o.

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