M2 January 2010 Q3
3. A particle of mass 0.5 kg is projected vertically upwards from ground level with a speed of 20 m s\(^{-1}\). It comes to instantaneous rest at a height of 10 m above the ground. As the particle moves it is subject to air resistance of constant magnitude \(R\) newtons. Using the work-energy principle, or otherwise, find the value of \(R\). (6)
| Scheme | Marks |
|---|---|
| \(\frac{1}{2} \times 0.5 \times 20^2\ ;\quad 0.5g \times 10\) | B1 B1 |
| \(10R = \frac{1}{2} \times 0.5 \times 20^2 - 0.5g \times 10\) | M1 A1 |
| \(\Rightarrow R = 5.1\) | DM1 A1 |
| (6 marks) |