RI 2020 A-Level H2 Phys Solution

RAFFLES INSTITUTION YEAR 5-6 PHYSICS DEPARTMENT 1 2020 A-Level H2 Physics Suggested Solutions Paper 1 1 B π= 34 3Vr ∆∆  ×= ×     100% 3 100%Vr Vr A graph of ∆ × 100%V V against ∆ × 100%r r will give a straight line graph through the origin. 2 D The action-reaction forces in Newton’s third law must be the same type and act on 2 different bodies. Option D: The weight of a car and the normal contact force on it are 2 forces acting on one single body i.e. the car. In addition, weight is a gravitational force which is not of the same type of force as the normal contact force. 3 D = forcestress area and = extensionstrain original length − − = × = × = = × = 2 1 2 3 force extensionunits of area under graph units of unit s of area original length Nm mm J m (since work done force displacement)m J m 4 A At = 0t , car X and car Y are at the same position. When car Y overtakes car X at =tT , the displacement of both cars from their position at = 0t is the same. Since the area under the velocity-time graph gives the displacement, ++=++ = =area under graph of car Y area under gr PQR aph o QR f car X S PS 5 C Note that = 3cbvv and the velocity of the bicycle relative to the car is given by − bcvv . 6 C Torque is a vector quantity. The statement in option C is unclear as the directions of the torques are not stated. A correct statement should read ‘The anticlockwise torque provided by the vertical forces is equal to the clockwise torque provided by the horizontal forces.’

RAFFLES INSTITUTION YEAR 5-6 PHYSICS DEPARTMENT 2 7 B θ = × = × torque of couple perpendicular distance b etween the parallel forces sin F Fd 8 A When balloon is inflated with hot air, ρ = + = +120 total weight, weight of hot air weight of basket and non inflated balloonW Vg mg ρ = = 20 upthrust on inflated balloon, weight of the atmospheric air displacedairU Vg Consider the free body diagram of the inflated balloon with basket. = + 2airU WT ( ) ( )( ) ( )( ) ρρ −= −+= = −− = = 20 120 2 2 1.204 2800 0.898 2800 7002 769.104 0.77 kN (2 s.f.) airUWT Vg Vg mg g (The answer should be 0.769 kN if rounded off to 3 s.f. However, the answer given in the option is 0.770 kN. This will be the best option to choose.) 9 D ( )( ) 3rate at which useful work is done by driving force 1.6 10 22 WFv= = × ×= 63.3 10rate at which total thermal energy is produced W60 ( )( ) ( ) × = = × 3 6 1.6 10 22 % efficiency 64 % 3.3 10 60 10 B ( ) 2 2 2 8 32 2 23.85 10 27.3 24 60 60 2.73 10 m s car r T ω π π −− = =  = ×  ××× = × 11 B The minute hand takes 1 hour to make one round the clock. ππω −−= = = × × 3122 1.75 10 rad s60 60T d F F

RAFFLES INSTITUTION YEAR 5-6 PHYSICS DEPARTMENT 3 12 A  − =− −−   = −+ = 12 12 12 12 12 2 2 22 2 final initial Gm m Gm mUU rr Gm m Gm m rr Gm m r Since >12 02 Gm m