SRMJEEE 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. State Newton's first law of motion and the concept it defines.

   A body continues in its state of rest or uniform motion in a straight line unless acted upon by a net external force. It defines inertia and inertial frames.

2. State Newton's second law of motion in terms of momentum.

   The rate of change of momentum is proportional to the applied force and is in the direction of the force: $$\vec{F} = \frac{d\vec{p}}{dt} = m\vec{a}.$$

3. State Newton's third law of motion.

   To every action there is an equal and opposite reaction; the forces of two bodies on each other are equal in magnitude and opposite in direction, acting on different bodies.

4. What is a free body diagram (FBD)?

   A diagram representing a single body in isolation with all external forces (and their directions) acting on it shown as vectors, used to apply Newton's laws.

5. State the law of conservation of linear momentum.

   In the absence of a net external force, the total linear momentum of a system remains constant: $\vec{p}_{\text{initial}} = \vec{p}_{\text{final}}$.

6. What is impulse, and how is it related to momentum?

   Impulse $= \vec{F}\,\Delta t = \int \vec{F}\,dt$, and by the impulse-momentum theorem it equals the change in momentum: $\vec{J} = \Delta\vec{p}$.

7. Distinguish between static, limiting, and kinetic friction.

   Static friction is self-adjusting and opposes impending motion (up to a maximum). Limiting friction is its maximum value just before sliding. Kinetic (dynamic) friction acts during sliding and is slightly less than limiting friction.

8. Define the coefficients of static and kinetic friction.

   $\mu_{s} = \dfrac{f_{s,\max}}{N}$ and $\mu_{k} = \dfrac{f_{k}}{N}$, where $N$ is the normal reaction. Generally $\mu_{s} > \mu_{k}$.

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

   The angle of friction $\lambda$ is the angle between the resultant of friction and normal reaction and the normal. $\tan\lambda = \mu_{s}$.

10. What is the angle of repose and its relation to friction?

    The angle of repose $\alpha$ is the minimum inclination at which a body just begins to slide down. It equals the angle of friction: $\tan\alpha = \mu_{s}$.

11. For a vehicle on a flat (unbanked) curved road, what is the maximum safe speed?

    $$v_{\max} = \sqrt{\mu_{s}\,r\,g},$$ where friction alone provides the centripetal force.

12. For a frictionless banked road, what is the relation between banking angle and safe speed?

    $$\tan\theta = \frac{v^{2}}{rg},\quad\text{so}\quad v = \sqrt{rg\tan\theta}.$$

13. For a banked road with friction, what is the maximum safe speed?

    $$v_{\max} = \sqrt{\,rg\,\frac{\mu_{s} + \tan\theta}{1 - \mu_{s}\tan\theta}\,}.$$

14. Define work done by a constant force and give its formula.

    Work is the product of force and displacement in the direction of the force: $W = \vec{F}\cdot\vec{d} = Fd\cos\theta$, where $\theta$ is the angle between force and displacement.

15. State the work-energy theorem.

    The net work done on a body equals the change in its kinetic energy: $$W_{\text{net}} = \Delta KE = \tfrac{1}{2}mv^{2} - \tfrac{1}{2}mu^{2}.$$

16. Write the formulas for kinetic energy and gravitational potential energy.

    Kinetic energy $KE = \tfrac{1}{2}mv^{2}$ and gravitational potential energy (near Earth) $PE = mgh$.

17. What is a conservative force? Give two examples.

    A force is conservative if the work it does is path-independent and equals zero over any closed loop (and can be derived from a potential energy). Examples: gravitational force and elastic spring force.

18. How is a conservative force related to potential energy?

    $$F = -\frac{dU}{dx},$$ i.e. the force is the negative gradient of potential energy.

19. What is the potential energy stored in a stretched/compressed spring?

    $$U = \tfrac{1}{2}kx^{2},$$ where $k$ is the spring constant and $x$ is the displacement from the natural length.

20. Distinguish 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.

21. For a 1-D elastic collision, what are the final velocities of two masses?

    $$v_{1} = \frac{m_{1}-m_{2}}{m_{1}+m_{2}}u_{1} + \frac{2m_{2}}{m_{1}+m_{2}}u_{2},\qquad v_{2} = \frac{m_{2}-m_{1}}{m_{1}+m_{2}}u_{2} + \frac{2m_{1}}{m_{1}+m_{2}}u_{1}.$$

22. Define the coefficient of restitution $e$ and its values for elastic and perfectly inelastic collisions.

    $$e = \frac{\text{relative velocity of separation}}{\text{relative velocity of approach}}.$$ $e = 1$ for perfectly elastic, $e = 0$ for perfectly inelastic, and $0 < e < 1$ in general.

23. Define the centre of mass and give its position formula for a system of particles.

    The centre of mass is the point where the total mass may be considered concentrated. Its position is $$\vec{R}_{cm} = \frac{\sum m_{i}\vec{r}_{i}}{\sum m_{i}}.$$

24. Define torque (moment of force) and give its formula.

    Torque is the turning effect of a force about an axis: $\vec{\tau} = \vec{r}\times\vec{F}$, with magnitude $\tau = rF\sin\theta$, where $\theta$ is the angle between $\vec{r}$ and $\vec{F}$.

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