2024 CCHY P2 PRELIM QP

2 2024 CCHY Preliminary Examination Physics (6091/02) / Sec 4 Express [Turn Over Section A Answer all the questions. 1 A hovercraft moves on a cushion of air which is trapped underneath it. The trapped air reduces friction. (a) The hovercraft starts from rest and, as it starts, the propeller produces a forward force F of 28 000 N. The mass of the hovercraft is 25 000 kg. Calculate the initial acceleration of the hovercraft. You may assume there is no friction. acceleration = .................................. [2] (b) Some time later, the hovercraft reaches a steady velocty, even though the force F is unchanged. Explain, in terms of forces acting on the hovercraft why the velocity is now constant. ....................................................................................................................................... ....................................................................................................................................... ................................................................................................................................... [2] [Total: 4]

3 2024 CCHY Preliminary Examination Physics (6091/02) / Sec 4 Express [Turn Over 2 There is no atmosphere on the Moon. An astronaut on the Moon drops a feather and a hammer from the same height at the same time. They both accelerate downwards at 1.6 m/s 2 and hit the ground at the same time. (a) The weight of the hammer is much larger than that of the feather. Explain why their accelerations are equal. ...................................................................................................................................... ....................................................................................................................................... ....................................................................................................................................... ....................................................................................................................................... ....................................................................................................................................... .................................................................................................................................... [3] (b) The feather takes 1.5 s to fall to the ground from rest. (i) Calculate the velocity of the feather as it hits the ground. velocity = ......................................................... [2]

4 2024 CCHY Preliminary Examination Physics (6091/02) / Sec 4 Express [Turn Over (ii) On Fig. 2.1, draw the velocity-time graph of the feather. Mark on the vertical axis, the velocity of the feather at time t = 1.5 s. Fig. 2.1 [1] (iii) Using the velocity-time graph in (b)(ii), determine the height from which the objects are dropped. height = ....................................................... [2] [Total: 8] time / s 0 0 1.5 velocity m / s

5 2024 CCHY Preliminary Examination Physics (6091/02) / Sec 4 Express [Turn Over 3 Fig. 3.1 shows a chair resting on a smooth ground. A horizontal force F keeps the chair balanced. C is the centre of gravity of the chair and the weight of the chair is 70 N. Fig. 3.1 (a) State the principle of moments. ....................................................................................................................................... ....................................................................................................................................... .................................................................................................................................... [2] (b) Calculate the force F applied to keep the chair balanced. force F = ........................................... [2] (c) Small metal discs were added to the bottom of the legs of the chairs, causing the position of the centre of gravity of the chair to shift from C to D. Explain why force F is no longer required to prevent the chair from toppling if the position of the centre of gravity shifts from C to D. ....................................................................................................................................... ....................................................................................................................................... .................................................................................................................................... [2] [Total: 6]

6 2024 CCHY Preliminary Examination Physics (6091/02) / Sec 4 Express [Turn Over 4 Fig. 4.1 shows a container of gas connected to a manometer. The tube in the manometer has a constant cross-sectional area. (a) Define the term pressure. ....................................................................................................................................... ....................................................................................................................................... .................................................................................................................................... [1] gas container ruler 30 cm 25 20 15 10 5 0 mercury Fig. 4.1

7 2024 CCHY Preliminary Examination Physics (6091/02) / Sec 4 Express [Turn Over (b) The density of mercury is 1.4 × 104 kg / m3. The gravitational field strength g is 10 N/kg. The pressure of the atmosphere is 1.0 × 105 Pa. Calculate the pressure in Pa of the gas in the container. pressure = ......................................... [3] (c) In Fig. 4.1, the mercury level on the left-hand side of the manometer is lower than on the right hand side. The gas inside the container is heated. This causes the mercury levels on both sides to become the same. (i) Mark on the ruler in Fig. 4.1 with a cross (x) when this happens. ................................................................................................................................ [1] (ii) Explain, in terms of the gas molecules, what causes the level of mercury to become the same. .................................................................................................................................. ..................................................................................................................................