2024 NASS Sc(Phy) P1 ANS

1 Sec 4 Preliminary Examination 2024 Ngee Ann Secondary School 2024 Sec 4 Science (Physics, Chemistry) (5086) Prelim Paper 1 (Physics component) 1 A 6 A 11 A 16 A 2 D 7 D 12 C 17 C 3 C 8 B 13 B 18 D 4 B 9 C 14 A 19 B 5 D 10 C 15 D 20 C Qn Solution Ans 1 Vector quantities are quantities with both magnitude and direction only. From the list given, the vector quantities are: force, acceleration, velocity, moment. A 2 Time taken by the car to travel a distance of 800 m = 2 min 1 sec – 1 min 35 sec = 61 – 35 = 26 s Average speed = distance travelled / time taken = 800 / 26 = 31 m / s (2 sf) D 3 Concept: Gradient of speed-time graph = acceleration. Hence, the section that corresponds to uniform acceleration will be the section of the speed-time graph with constant gradient (a straight line graph) Uniform acceleration = gradient of straight line graph between time = 2 s and time = 3 s = (20 – 10) / (3 – 2) = 10 m / s 2 C

2 Sec 4 Preliminary Examination 2024 4 Mass is the amount of matter in a body. Since there is no change in the amount of matter in the astronaut at all times, the mass is a constant, regardless of location. From surface of Earth to the space, the gravitational field strength of Earth decreases. Since weight = mass x gravitational field strength, the weight will decrease. B 5 Both the watermelon and the durian have the same ma ss and hence the same weight. The force exerted by the durian on the plastic bag will be equal to that exerted by the watermelon on the plastic bag. But the surface area of contact between the watermelon and plastic bag is larger than that between the durian and plastic bag. Since pressure = force / area, the pressure exerted by the durian on the plastic bag will be larger and hence the plastic bag is likely to tear. D 6 The resultant of the three forces is zero. But since the object is already in the state of motion and moving to the right before the three forces applied, by Newton’s 1 st Law, the object will continue to move with a constant speed along a straight line (and in the same direction). A 7 There is no other force acting on the toy, except weight of the toy. Hence, in order for the toy to be balanced, the line of action of weight of the toy should pass through the support so that the moment due to the weight of the toy will be zero (and does not cause any turning effect). Hence, centre of gravity of the toy should be at point D. D 8 Work done = force x distance travelled in the direction of the force = 2000 x (5.0 x 103) = 10 000 000 J = 10 MJ B 9 Since particles are close together and moving past each other at random, this tells us that the substance is in a state of liquid. Hence, the substance is changing from liquid to gas. During the change in the state of matter, the temperature is a constant. Hence, the internal kinetic energy of particles will be constant. C

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