Kinematics – JEE Mains Physics

• by Zenith LMS
• Updated April 2025

1. Frame of Reference

• A frame of reference is a coordinate system along with a clock used to describe and measure motion.
• It is necessary to specify a reference frame to study the motion of an object.
• Motion is always relative to the chosen frame of reference.

2. Motion in a Straight Line

• Also called one-dimensional motion.
• Examples: A car moving along a straight road, a ball dropped from a height.

3. Speed and Velocity

• Speed: The rate of change of distance with time; scalar quantity.
• Velocity: The rate of change of displacement with time; vector quantity (has both magnitude and direction).

4. Uniform and Non-Uniform Motion

• Uniform Motion: When an object covers equal distances in equal intervals of time.
• Non-Uniform Motion: When an object covers unequal distances in equal intervals of time.

5. Average Speed and Instantaneous Velocity

• Average Speed = Total distance / Total time.
• Instantaneous Velocity: Velocity of an object at a particular instant of time.

6. Uniformly Accelerated Motion

• Acceleration is constant in magnitude and direction.
• Important formulas:

  v = u + at s = ut + ½at² v² = u² + 2as s = [(u + v)/2]·t

  Where,
  u = initial velocity,
  v = final velocity,
  a = acceleration,
  s = displacement,
  t = time.

7. Velocity-Time and Position-Time Graphs

• Velocity-Time Graph:
  • Area under the graph gives displacement.
  • Slope gives acceleration.
• Position-Time Graph:
  • Slope gives velocity.

8. Relative Velocity

• Velocity of one object with respect to another.
• In one dimension:

  v(AB) = v(A) - v(B)

• Important in analyzing problems involving two moving bodies.

9. Motion in a Plane

• Two-dimensional motion: Requires two coordinates (x and y) to describe position.
• Example: A ball thrown at an angle, motion of a bird.

10. Projectile Motion

• A type of two-dimensional motion under constant acceleration due to gravity.
• Key points:
  • Horizontal velocity remains constant (ignoring air resistance).
  • Vertical velocity changes due to gravity.
  • Path followed is a parabola.
• Important Formulas:

  Time of flight (T) = (2u sinθ)/g Maximum height (H) = (u² sin²θ)/(2g) Horizontal range (R) = (u² sin2θ)/g

11. Uniform Circular Motion

• When an object moves in a circle at constant speed.
• Although speed is constant, velocity changes due to change in direction.
• Important quantities:
  • Angular velocity (ω) = θ/t
  • Centripetal acceleration (a_c) = v²/r