2023 XMS P2 PRELIM MS

Xinmin Sec 2023 Prelim 4E Physics 6091/02 Section A Qns Answers Remarks 1a Two vertical forces that are seemingly equal in length [B1] -- Weight -- Upthrust F/U Do not accept NCF/NRF, accept friction (with water) or (water) resistance Accept reasonable symbols 1bi The weight of the block is equal [A1] to the weight of liquid displaced by the block. Upthrust = Weight of block (from 3a) Upthrust = Weight of liquid displaced (from question) So, W block = W liquid displaced 1bii The weight of water displaced is equal [A1] to the weight of diesel displaced. W block in water = W block in diesel So, W water displaced = W diesel displaced 1c W water displaced = W diesel displaced m water x g = m diesel x g [½ for W = mg] ρ water x V water = ρ diesel x V liquid D [½ for m = ρV] ρ water x 75% x V block = ρ diesel x 86% x V block [M1] (1000) (0.75) = (ρ diesel) (0.86) ρ diesel = 872 kg/m3 [A1] From 3bii g will cancel off [1 for relating Vliquids to Vblock] Vblock will cancel off FULL MARKS IF NO WORKING BUT CORRECT ANSWER Total 6m 2ai direction of over-turning moment is clockwise [A1] 2aii clockwise moments = (U x 36) + (T x 20) = (400k x 36) + (45k x 20) = 15 300 kNm [M1] anti-clockwise moment = (W x 20) = (400k x 20) = 8000 kNm resultant moment = 15 300 – 8000 = 7300 kNm [A1] 2b Put the heavier cargo at the lower decks and lighter cargo at the upper decks. [A1] Lowers the CG Total 4m 3a P = ρgh = 1000 x 10 x 2 = 20 000 Pa [M1] F = PA = 20 000 x 0.02 [M1] = 400 N [A1] 3b Upward forces = Downward forces Normal contact forces by slabs = Force by water + Weight = 400 + 19 [M1] = 419 N [A1] upwards [A1] Total 6m 4a - The water at the bottom, nearest the heater is heated and expands. - This water becomes less dense and rises. - The comparatively cooler and denser cooler water at the top is displaced and sinks to come near the heater. - The process repeats and convection currents are set up. Any 2 points for [1m] 4b [A1] Styrofoam / cork / rubber / plastic [B1] This material contains air pockets. Air/rubber/plastic is a poor conductor of heat, so heat loss by conduction is reduced. Accept any possible answers. 4c [A1] White and smooth/shiny/glossy [B1] Light colours and smooth textures are poor emitters of heat, so heat loss by radiation is reduced. Accept any light colours besides white. Total 6m

5a 30°C --- 0.5 mV 66°C --- 0.5 / 30 x 66 [M1] = 1.1 mV [A1] 5b The higher the temperature T, (the lower the resistance of the thermistor) the smaller the potential difference across it. [A1] (emf divides amongst resistors in series proportionately) Accept opposite / vice versa. Total 3m 6a 50 complete waves are produced in 1 second. [B1] 6b 5 waves – 30 m ➔ 𝜆 = 6 m [M1] v = f 𝜆 = 50 x 6 = 300 m/s [A1] 6c The more shallow the water / the smaller the depth of water (the smaller the wavelength) the slower the wav