DHS 2023 Prelim Physics (Paper 2 Solutions)

DUNMAN HIGH SCHOOL 2023 H2 PHYSICS (YEAR 6) 1 Answers to Prelim Exam H2 Physics Paper 2 Qn Answer Marks 1(a) Speed is a physical quantity and can only be defined in terms of other physical quantities. Distance is a physical quantity, but second is a unit for time which cannot be used to define speed. B1 B1 1(b) Vertically, from v = u + gt and taking upward as positive, −u sin = u sin − gT M1 Time of flight, 2 sin2 uTt g == M1 Horizontally, from s = ut 2 ( cos )( ) 2 sin ( cos ) 2 sin cos R u T uu g u g    = =  = A1 A0 Marker’s comments: It is a “show” type of question and thus important that all steps, including substitution must be explained and shown. 1(c) Maximum R occurs when sin2 1 = . Hence 45o = A1 1(d) 2 0 uR g= ( ) ( )( ) 145.36 1000 m45.36 km 12.6 m s1 h 60 60 s −== ( ) 2 0 2 2 12.6 16.3 9.7399 m s ug R − = = = 0 0 2 Rgu g u R  =+ C1 A1 T

DUNMAN HIGH SCHOOL 2023 H2 PHYSICS (YEAR 6) 2 2 3429.7399 100 100 0.97 1 m s (to 1 s.f.) g g −  =+  = = Therefore, ( )10 1g = m s−2 A1 A1 Marker’s comments: Uncertainty should only be left to 1 sig fig. The final answer and its uncertainty should have the same d.p. It is important to convert the speed to m s−1 to obtain g in units of m s−2. Also, there were mistakes in understanding the meaning of percentage uncertainty. 2(a) The upthrust is the resultant upward force due to the larger pressure exerted by the fluid at the bottom compared to the top surface of the body. B1 2(b) ( ) displaced fluidUpthrust 8001050 9.818000 1030 N (shown) fluid cannon W Vg = = =  = M1 A0 Marker’s comments: It is a “show” type of question and thus important that all steps, including substitution must be explained and shown. 2(c) The rate of change of momentum of a body is directly proportional to the resultant force acting on the body and occurs in the direction of the resultant force. B1 2(d) During its upward motion, the cannon experiences viscous drag force which acts in the opposite direction of its motion and increases with the speed of the cannon. Net force on canon = upthrust – (weight + drag force) decreases (since weight and upthrust are constant) Since the net upward force decreases over time, the momentum increases non-linearly (since the net force is directly proportional to the rate of change of momentum) B1 B1 Marker’s comments: Very often, drag force is not mentioned. There were misconception that the upthrust decreases causing net force to decrease or the velocity decrea