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Calculus in kinematics

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Displacement, velocity and acceleration are linked by differentiation and integration.

The chain of links

Differentiate to go down: s โ†’ v โ†’ a
v = dsdt, a = dvdt
Integrate to go up: a โ†’ v โ†’ s

At rest and maximum speed

A particle is at rest when v = 0.
Velocity is greatest or least when a = 0.

Using conditions

When you integrate, add a constant and find it from a given value.
a = 4 โˆ’ 2t, v = 5 when t = 0: v = 4t โˆ’ t2 + c, and c = 5.
Worked example

s = t3 โˆ’ 6t2 + 9t. Find when the particle is at rest.

  1. v = 3t2 โˆ’ 12t + 9
  2. 3(t2 โˆ’ 4t + 3) = 0
  3. 3(t โˆ’ 1)(t โˆ’ 3) = 0

Answer: t = 1 and t = 3

Key idea

v = dsdt, a = dvdt. Integrate to reverse, and use given values to find the constant. At rest: v = 0.

The interactive lesson includes the diagrams for this topic.

Check you have got it

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