CJC 2019 A level H2 Physics Answers

1 H2 Physics 9749 – 2019 A Level Exam Paper 1 1 Essential Question(s): What does the unit prefixes represent? Solution: nano - 10-9 micro - 10-6 milli - 10-3 centi - 10-2 deci - 10-1 kilo - 103 giga - 109 Answer: D 2 Essential Question(s):  What does accuracy ±1% mean?  What does “additional” uncertainty of ±10 mV mean?  When recording value together with its uncertainty, how do we represent the absolute uncertainty and how does the value be represented? Solution: The overall absolute uncertainty = 1 % of the value recorded PLUS 10 mV,     3V 4.072 0.01 10 10 0.0502V V 0.05V          Rounding up the uncertainty to reflect the full statement of “additional 10 mV”, and to represent absolute uncertainty to 1 significant figure. Subsequently, the next step is to truncate the value to the same decimal place as the absolute uncertainty,  V V 4.07 0.05 V   Answer: D 3 Essential Question(s):  How to construct the equations of motion using the information provided? Solution: From Start to (t-1)seconds S1 = ½ a (t-1)2 – (1) From Start to t seconds S2 = ½ a (t)2 – (2) (2) / (1) :

2 2 1 22 2 2 1 ( 1)2 1 ( )2 0.25 ( 1) 1 ( ) 1 ( 1) 2 ( ) 2 a tS S a t t t t t t      Answer: D Examiner’s comments: Candidates performed well on this question demonstrating string understanding of kinematics 4 Essential Question(s): o How is the speed and acceleration related to the displacement time graph? o How does acceleration changes in a free fall with air resistance? Solution: Speed increases. Gradient of the graph is increasing. Speed increases at a decreasing rate because the air resistance is increase but the weight is constant. Resultant force decreases and so acceleration decreases. Answer: C 5 Essential Question(s):  How is the conservation of linear momentum applied here? Solution: Initial momentum is zero. So X being less mass move at higher speed, and Y being higher mass moves at lower speed. But the product of the speed and mass is the same. So the centre of mass remains at the same position. Answer: A Examiner’s comments: Options C or D were popular incorrect choices. As the total momentum o f the system is zero before the explosion, the centre of gravity cannot move. If it does, this would mean that an external force must have been applied to the system, which is not the case in this question. 6 Essential Question(s): o Since it is inelastic collision, what are the physics concepts to be used? Solution: Conservation of linear momentum: mu = mv + 2mv u = 3 v

3       2 2 2 2 2 2 2 2 1 1 1( ) ( ) (2 )Initial Total KE Final Total KE 2 2 2 1Initial Total KE ( )2 (3 ) ( ) (2 ) (3 ) 9 1 4 9 4 9         m u m v m v m u v v v v Answer: B 7 Essential Question(s):  What is Hooke’s Law?  How to calculate the work done?  Solution: Hooke’s Law is obeyed when t