M2 June 2017 Q6
6.

The points \(A\) and \(B\) lie 40 m apart on horizontal ground. At time \(t = 0\) the particles \(P\) and \(Q\) are projected in the vertical plane containing \(AB\) and move freely under gravity. Particle \(P\) is projected from \(A\) with speed 30 m s\(^{-1}\) at 60\(^\circ\) to \(AB\) and particle \(Q\) is projected from \(B\) with speed \(q\) m s\(^{-1}\) at angle \(\theta\) to \(BA\), as shown in Figure 4.
At \(t = 2\) seconds, \(P\) and \(Q\) collide.

| Scheme | Marks |
|---|---|
| \(30\cos 60 \times 2 + q\cos\theta \times 2 = 40\) | M1 A1 |
| \(30\sin 60 \times 2 - 4.9 \times 4 = q\sin\theta \times 2 - 4.9 \times 4\) \(30\sin 60 = q\sin\theta\) | M1 A1 |
| \(q\cos\theta = \pm 5\) \(q\sin\theta = 15\sqrt{3}\) | |
| \(\tan\theta = 3\sqrt{3}\) \(\left(\tan\theta = 6\sin 60\right)\) | DM1 |
| \(\theta = 79.1\ \ (79)\) | |
| \(q = 26.45... = 26.5\) | A1 |
| (6) |
Notes
M1 Equation for horizontal distance. Need to be using the 40 m
A1 Correct unsimplified
M1 Equal vertical distance or initial vertical components of velocity
A1 Correct unsimplified (no error seen)
DM1 Solve for \(q\) or \(\theta\). Dependent on both preceding M marks
(1.38 radians) or better
A1 (26 or better) \(\left(10\sqrt{7}\right)\) Both correct and no error seen
| Scheme | Marks |
|---|---|
| Vertical component of speed = | M1 |
| \(30\sin 60 - 2g\ (= 6.38...)\) | A1 |
| speed \(= \sqrt{(30\cos 60)^2 + 6.38^2}\) | DM1 A1ft |
| \(= \sqrt{15^2 + 6.38^2} = 16.3\) (m s\(^{-1}\)) | A1 |
| (5) | |
| (11 marks) |
Notes
M1 Must be working towards speed of \(P\) (or \(v^2\)) (condone if working on \(Q\) - they equal vertical components of velocity)
A1 Correct unsimplified. Accept \(\pm\)
DM1 Use Pythagoras. Dependent on previous M. Follow their vertical component.
A1ft Correct unsimplified equation in \(v\) or \(v^2\).
A1 or 16 2 or 3 sf only
6b alt
| Vertical distance = | M1 |
| \(30\sin 60 \times 2 - 4.9 \times 4 = 32.36\) | A1 |
| Conservation of energy: | DM1 |
| \(\dfrac{1}{2}mv^2 + mg \times 32.36 = \dfrac{1}{2}m \times 900\) | A1ft |
| \(v = 16.3\) (m s\(^{-1}\)) (16) | A1 |
M1 Must be working towards speed of \(P\)
A1 Correct unsimplified
DM1 Dependent on previous M. Follow their vertical distance.
A1ft Correct unsimplified equation in \(v\) or \(v^2\).