2022 SJI Phy Prelims P1&2 Ans

2022 Physics Prelim Exam Marker’s Report Paper 1 1 D 11 D 21 C 31 C 2 B 12 C 22 D 32 B 3 C 13 A 23 A 33 B 4 B 14 C 24 C 34 D 5 A 15 C 25 A 35 C 6 C 16 A 26 B 36 C 7 C 17 D 27 D 37 B 8 C 18 D 28 C 38 B 9 B 19 A 29 B 39 A 10 A 20 D 30 C 40 D Paper 2 1 Fig. 1.1 shows how the speed of SpaceX, a rocket varies with time as it enters the gravitational field of a new Planet Y with negligible atmosphere. SpaceX has a total mass of 1.8 x 106 kg. Once it enters the atmosphere of Planet Y, it undergoes free fall for 8.0 s before its engine fires a continuous thrust to bring it to a gentle upright landing on the surface of Planet Y. Fig 1.1 (a) Calculate the weight of Space X on Planet Y. a=(v-u)/t = (82-10)/8 = 9.0 m/s2 W=mxg = 1.8 x 106 kg x 9.0 N/kg =1.62 x 107 N weight = ……………………..[2]

2 (b) At 8.0 s, significant amount of liquid Oxygen fuel undergoes combustion in the rocket engine to produce a constant thrust, T to decrease space X’s speed of descent. (i) On Fig. 1.2, draw and label all the forces acting on SpaceX during its descent. You may ignore air resistance. [1] Fig. 1.2 (ii) Hence, calculate the magnitude of the thrust, T. Taking upward as the positive direction Fresultant = T – W 1.8 x 106 kg x 4.1 N/kg = T – (1.62 x 107N) R =23.58 x 106 N = 2.36 or 2.4 x 107 N ecf allowed from (a) for W T = ………………….. [2] (iii) In reality, from t = 8.0 s to t = 28.0 s, the deceleration of SpaceX is increasing. Assuming that the thrust produced by the engine is uniform, explain in terms of forces why this is so. As the shuttle lands, its mass/weight decreases due to the burning of fuel, hence the upright resultant force is increasing (as thrust is constant) and deceleration is increasing ………………………………………………………………………………[1] T W

3 2 A man standing in a hot air balloon dropped a ping pong ball as the balloon accelerated upwards at 2.0 m/s2. The speed of the balloon is 2.0 m/s at the moment the ping pong ball is released. Assuming that the ping pong ball has the same velocity as the balloon when it is released. Fig. 2.1 shows how the velocities of the h ot air balloon and the ping pong ball vary with time. Fig. 2.1 (a) (i) Explain why the acceleration of the ping pong ball at its maximum height is 10 m/s2. ● The ping pong ball is momentarily at rest, hence there is no air resistance acting on it. ● The only force acting on the ball is weight as such it experiences acceleration due to gravity only which is 10 m/s2. ………………………………………………………………………………[2] (ii) Describe how the acceleration of the ping pong ball changes from the moment it is released until it reaches its terminal velocity. ● The gradient of the graph decreases to 0 at 2.2 s. Showing that acceleration is decreasing throughout the motion. ● The acceleration is zero (a= 0 m/s2) at t=2.2 s. …