RI 2023 Promo H2 Physics Solutions

Raffles Institution Year 5-6 Physics Department 1 2023 Year 5 H2 Physics Promotional Examination Solution Section A Qn Ans Solution 1 B 3 344 3 32 3 dVr Vd VV ππ = =  ∆∆ = Gradient of the graph is 3. 2 D milli – 310− micro – 610− nano – 910− 3 C bus bus 12 30 360 ms ut= =×= ( ) 2 car car 2 2 1 2 1360 12 3.2 0 30 2 0.83378 0.83 m s s u t at a a − = + ++ = + = = 4 A from velocity-time graph, 1 0.15 0.2 0.35 m s v − ∆= − − = By Newton’s third law, ( ) ( )( ) ( ) force on cart force on sensor impulse on cart area under force-time graph of sensor 1 0.08 0.02 402 0.35 1.2 3.4286 3.4 kg mv m m =− =− ∆= − − −= − = = 5 D Option A (incorrect): Upthrust on an object is equal to its weight only if the object is floating (i.e. in equilibrium). Option B (incorrect): Upthrust does not depend on the mass of the object. It depends on the mass and hence the volume of the liquid displaced by the submerged object. The volume of liquid displaced depends on the volume of the fully submerged object, which can be different even if the two objects have the same mass. Option C (incorrect): Upthrust is due to the difference in fluid pressure at the top and bottom surfaces of the object. Option D (correct): Upthrust is numerically equal to the weight of the liquid displaced by the submerged object. Hence upthrust depends on the density of the liquid and the volume of the liquid displaced. Since both spheres have the same dimensions, both displace the same volume of liquid when fully submerged and hence experience the same upthrust.

Raffles Institution Year 5-6 Physics Department 2 6 C Taking moments about O, ( ) ( )4 sin sin cos 3sin cos 1tan 3 18.435 18.4 mg L mg L Lθ θθ θθ θ θ = + = = = = ° 7 C Power is the rate of transfer of energy. Hence the gradient of the graph is power. Maximum power occurs between 4 st = to 6 st = , when the gradient is the largest. 40 10maximum power output to lift container 15 kW64 −= = − Since power outputefficiency power input= , power output 15power input (supplied) 23.077 23 k Wefficiency 0.65= = = = 8 B ( ) 11 41 2 2 1.50 10 365 24 60 60 29886 2.99 10 m s vr rT ω π π − = = × = ××× = = × 9 A The centripetal force on the ball is the resultant of the contact force and weight. The centripetal force points horizontally towards the centre of the horizontal circle. 10 C Work done by the gravitational force, () 31 2 2 g extFF fi WW m GM GM RR GM R φφ =− = −−  = − − −−   = P Q R O L L L mg 4mg tabletop N W

Raffles Institution Year 5-6 Physics Department 3 11 A By conservation of energy, surface infinity 21 02 escape EE GMm mvR = −+ = 3 22 4228 3 3 escape escape GRGMv GR v RRR ρπ πρ ρ  == = ⇒∝ 2 , 2 , 2 , 1 41 (11.2)54 2.5044 2.50 km s escape M MM escape E EE escape M v R v R v ρ ρ − =   =     = = 12 D Option A (