Physics Lens

02. Kinematics

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  • Displacement is the distance travelled along a specified direction.
  • Speed is the rate of change of distance travelled.
  • Velocity is the rate of change of displacement.
  • Acceleration is the rate of change of velocity.

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  • v=u+at
  • s=(u+v2)t
  • s=ut+12at2
  • v2=u2+2as

s: displacement
u: initial velocity
v: final velocity
a: acceleration
t: time

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  • Tip: Sometimes, you will require two equations to solve a kinematics problem. For a parabolic path in a projectile motion without resistive forces, you can draw a table such as the one below and fill in the blank with the information given in the question.
Initial velocity at an angle
Initial velocity at an angle
  • In the case where a projectile is launched at an angle θ to the horizontal and undergoes the acceleration of free fall, the various horizontal and vertical components of displacement, velocity and acceleration can be expressed in the following way:
Horizontal Vertical
displacement, s (ucosθ)t (usinθ)t+12gt2
initial velocity, u ucosθ usinθ
initial velocity, v ucosθ usinθ+gt
acceleration, a 0 g
time, t same for both dimensions

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