Physics 4321 [Paper 2 Section B]CHAPTER 2(2.8 Gravity)1. Diagram 9.1 shows the effect of a man falls from high position to the ground without opening the parachute. Diagram 9.2 shows a man with the same mass falls from the same height when the parachute is open.

(a) (i) What is the meaning of free fall? [ 1 mark] (ii) Based on diagram 9.1 and Diagram 9.2, compare the acceleration, the rate of change of momentum and the time of impact.Relate the rate of change of momentum with the time of impact to make deduction on the relationship between the acceleration and the rate of change of momentum. [ 5 marks]

(b) A hovercraft moves on a cushion of air which is trapped underneath it, as shown in Diagram 9.3. The trapped air reduces the friction. The hovercraft starts from rest and as it starts, the propeller produces a forward force until it reaches a constant velocity.

(i) Sketch a velocity-time graph to show the motion of hovercraft.

(ii) Explain why the hovercraft moves with constant velocity in terms of the force acting on it[4 marks]

You are required to give some suggestions to design a canoe which can travel faster andsafer . Using the knowledge on motion, forces and the properties of materials, explain the suggestions based on the following aspects:(i) the surface of the canoe(ii) the shape of the canoe(iii) the material of the canoe(iv) the material of the canoe(v) the material of the canoe[ 10 marks ]

2. Diagram 9.1 shows a car and a lorry stopping at a red traffic light. When the traffic light turns green as in diagram 9.2, the car is found to move ahead of the lorry.

(a) What is meant by mass? [ 1 mark ]

(b) Based on diagram 9.1 and 9.2, compare the masses of the vehicles and their ability to speed ahead. Relate the mass of the vehicle and the way it can start moving from rest to deduce a concept in physics with regard to the motion of objects.State the physics concept. [ 5 marks ]

(c) Based on the physics concept stated in (b), (i) explain why a driver lurch forwards when a car he is driving comes to a sudden stop, (ii) describe and explain a method which can overcome the situation in (c)(i). [ 4 marks ](d) Diagram 9.3 shows a water rocket made from an empty 1.5 litre plastic soft drink bottle by adding water and pressurizing it with air for launching.

The objective is to keep the rocket in the air as long as possible. Using the appropriatephysics concepts, suggest and explain suitable designs based on the characteristics of(i) the acceleration,(ii) the shape(iii) the structure(iv) the buoyant force (upthrust),(v) the stability of the motion, to improve the water rocket. [ 10 marks]

3. Diagram 11.1 shows Newtons cradle which consists of five identical balls suspended in a row from a wooden frame by wires.Diagram 11.1When the ball on left end is pulled aside (Diagram 11.2) and allowed to fall, the ball on the far end is knocked away from the others with the same speed as the first ball (Diagram 11.3).

(a) Name the physics principle involved which makes the ball on the other far end is knocked away from the others. [1 mark](b) Explain, in term of momentum and energy transfer, why the ball on the opposite end is knocked away from the others. [4 marks]

(c) Diagram 11.4 shows five designs of Newtons Cradle, P, Q, R, S and T, with differentspecifications. You are required to determine the most suitable design to make the ball at the end swings up to higher level and at bigger speed. Study all the five designs from the following aspects:(i) The arrangement of the balls(ii) The type of material used to make the balls(iiii) The number of string used to hang the balls(iv) The position of the ball to start the oscillationExplain the suitability of the aspects. Justify your choice.. [ 10 marks]

(d) In a game, a 50 g white ball of speed 0.8 m s-1 hits a 30 g red ball at rest . If the white ball stops after the collision, calculate;(i) the velocity of the red ball after the elastic collision.(ii) the change of the momentum of the white ball.(iii) the impulsive force acting on the white ball during the collision if it is stopped in 0.05 seconds. [5 marks]