Delayed-start overtaking twice

Delayed-start overtaking twice

Secondary 4
7 marks
Original parallel to supplied A Math Kinematics references

Particle \(P\) passes a fixed point \(O\) at time \(t=0\). Its velocity at time \(t\) seconds is \(2t\text{ m s}^{-1}\). Two seconds later, particle \(Q\) passes \(O\) in the same direction with constant velocity \(12\text{ m s}^{-1}\). Let \(T\) seconds be the time elapsed after \(Q\) passes \(O\).

  1. Express the displacements of \(P\) and \(Q\) from \(O\) in terms of \(T\).[2]
  2. Find the two values of \(T\) at which the particles meet.[3]
  3. State which particle overtakes the other at each meeting.[2]

Solution:

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Answer:(i) \(x_P=(T+2)^2\), \(x_Q=12T\); (ii) \(T=4\pm2\sqrt3\text{ s}\); (iii) \(Q\) overtakes \(P\) first, then \(P\) overtakes \(Q\)

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