Opposing power-law motions

Opposing power-law motions

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

Two particles \(P\) and \(Q\) lie on the same straight line. At time \(t=0\), \(P\) is at \(A\) and \(Q\) is at \(B\), where \(AB=24\) metres. They move towards each other. The velocity of \(P\) towards \(B\) is \(3\sqrt{t}\text{ m s}^{-1}\), while the velocity of \(Q\) towards \(A\) is \(t\text{ m s}^{-1}\).

  1. Taking distance from \(A\) towards \(B\) as positive, find the positions of \(P\) and \(Q\) at time \(t\).[2]
  2. Show that the particles meet when \(t=4\).[3]
  3. Find the distance of the meeting point from \(A\).[2]

Solution:

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Answer:(i) \(x_P=2t^{3/2}\), \(x_Q=24-\dfrac12t^2\); (ii) \(t=4\text{ s}\); (iii) \(16\text{ m from}\hspace{0.5em}A\)

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