(EJC) 2024 J2 H2 PRELIM Answers P1-3

©EJC 2024 9749/J2H2PRELIM/2024 EUNOIA JUNIOR COLLEGE JC2 Preliminary Examination 2024 9749 PHYSICS MARK SCHEME Paper 1 – Multiple Choice Questions Question Key Question Key Question Key 1 A 11 A 21 C 2 D 12 D 22 A 3 C 13 C 23 A 4 D 14 D 24 C 5 C 15 C 25 B 6 A 16 D 26 B 7 A 17 B 27 C 8 C 18 D 28 A 9 B 19 A 29 C 10 C 20 D 30 C 1 Answer: A Notice that the options are all given in electrical units, hence we express power in terms of potential difference and current. 2 unit for ( ) unit for unit for unit for ( ) Vk = I I unit for L 2 unit for ( ) unit for ( )unit for ( ) V R    = = =  I 2 Answer: D Velocity is a vector, thus the direction sign of the velocity when the ball is going up is the negative of the direction sign of the velocity when the ball is coming back down. Thus, reject option A and option B. Given the asymmetry of the height-time graph where the time taken for upward journey of ball is shorter than downward journey, air resistance must be present. Since work is continually done against air resistance, the final kinetic energy of the ball (just before hitting ground) would be less than the initial kinetic energy of the ball (when it was first thrown up from the ground). Also, the area under graph for the first part of graph should be same as that in the second part since the distance travelled up and down are the same. So, reject option C.

2 ©EJC 2024 9749/J2H2PRELIM/2024 3 Answer: C : yys u t+  = 21 2 : xx gt s u t + + → = Combining the 2 equations gives 2 1 2 x y x ssg u =   or x x ys u s Thus, 21 2 1.4112 A A A B B B x u s x u s= = = = 4 Answer: D For Z, FYZ = 4ma ……(1) For Y, FXY – FZY = 3ma ……(2) From Newton’s 3rd Law: FYZ= FZY= 4ma ……(3) From (2) & (3), FXY – 4ma = 3ma FXY = 7ma = FYX Thus, 77 44 YX ZY F ma F ma== F Z Y X FYX FXY FZY FYZ a a a 4m 3m m

3 ©EJC 2024 9749/J2H2PRELIM/2024 5 Answer: C 1 Newton's 2nd Law gives When string breaks, tension 0 ( ) ( ) 0 1000(1.0)(9.81) (800)(1.0)9.81 (800)(1.0) 2.45 m s net wood wood wood water wood wood wood wood F m a U m g T m a T V g V g m a a a  − = − − = = − − = −= = 6 Answer: A ( ) 2 2 22 Apply Newton's 2nd Law: At bottom, .....(1) At top, assume points downwards .....(2) From bottom to top, conservation of ener gy gives 1(2 ) .....(3)2 B B T T T BT mvN mg r N mvN mg r mg r m v v −= += =− (1)-(2), then substituting (3) gives 6 5.5 6 0.5 Negative sign indicates should point up wards, opposite to assumption. BT T T T N N mg N mg N mg N −= −= =− mg T U a mg NT mg NB vB vT

4 ©EJC 2024 9749/J2H2PRELIM/2024 7 Answer: A The work done by the net force provides the change in kinetic energy, which is equal to the