Error Logs

Physics - Mechanics Determine if the collision is elastic using kinetic energy calculations. My answer: Compared KE of A before with KE of B after. NO, it is in elastic collision. What's correct: Method error. Must compare the sum of kinetic energies of all objects before vs after (Total KE). The collision is indeed inelastic (total KE decreases), but the comparison was flawed. Marks lost: 2 Reference: a6c5a9c3-a383-5d3c-99a8-2f0e5c28717a

Physics - Mechanics Estimate and compare the average force of impact on Trolleys A and B. My answer: Force A = -1.26m N; Force B = -1.2m N. Different forces. What's correct: Unit error (ms^-1 for acceleration) and calculation errors. According to Newton's Third Law, forces must be equal in magnitude and opposite in direction (|F_A| = |F_B|). Marks lost: 3 Reference: a6c5a9c3-a383-5d3c-99a8-2f0e5c28717a

Physics - Mechanics Estimate the time of impact from a velocity-time graph. My answer: 1.6s (crossed out) What's correct: Self-correction error. The sharp velocity change at 1.6s is indeed the start of the impact. The answer was correct but discarded. Marks lost: 1 Reference: 9874e5b0-9827-5e11-aa2b-1ec4837f0cfa

Physics - Optics Find the object-lens separation for an erect image twice as large as the object. My answer: 1/v + 1/u = 1/f (formula only) What's correct: Failed to apply magnification M=2 (v=-2u) and f=3. 1/3 = 1/u - 1/2u => 1/3 = 1/2u => u = 1.5 cm. Marks lost: 1 Reference: 7f59ab7f-ef7b-5ad9-9f52-21fa549cb25d

Physics - Optics Draw refracted rays for incident rays q and r. My answer: Converged rays at (2cm, -2cm). What's correct: Calculation error. Using 1/f = 1/u + 1/v (f=3, u=8), v = 4.8cm. Image height = -1.2cm. Rays must converge at (+4.8, -1.2). Marks lost: 2 Reference: 7f59ab7f-ef7b-5ad9-9f52-21fa549cb25d

Physics - Optics Determine the focal length from a ray diagram where a parallel ray refracts through the axis. My answer: 8 cm What's correct: The parallel ray (p) passes through the principal axis 3cm from the lens (6 squares * 0.5cm). Focal length is 3 cm. Marks lost: 1 Reference: 7f59ab7f-ef7b-5ad9-9f52-21fa549cb25d

Physics - Optics Explain why the ground is seen lit by a torch. My answer: Yes, as light reflects back to his eyes. What's correct: Incomplete. Must name the phenomenon: Diffuse Reflection (or scattering). Rough surfaces reflect light in many directions, ensuring light reaches the eyes. Marks lost: 1 Reference: c92fd5f1-ae58-5596-8d20-0d41f30792fa

Physics - Optics Explain if Jones sees the lake is lit by his torch when shining it on a calm lake (plane mirror). My answer: No, the reflected rays can't reflect into Jones' eyes. What's correct: Yes. The lake acts as a plane mirror; light follows the Law of Reflection. If Jones is in the path, light enters his eyes and he sees the lit area. Marks lost: 2 Reference: c92fd5f1-ae58-5596-8d20-0d41f30792fa

Physics - Thermodynamics Write an expression for the SHC of the aluminium block in terms of M, m, c and measured temperatures. My answer: power supplied - mc / (measured T - initial T) M What's correct: Incorrectly included 'power supplied'. Using heat lost = heat gained: Cal = [m * c * (T_final - T_water_initial)] / [M * (T_block_initial - T_final)]. Marks lost: 1 Reference: 62eb10cb-80c0-5f3c-ba90-00da26a78dff

Physics - Thermodynamics Describe the procedure to find the specific heat capacity of an aluminium block. My answer: Heated water with an immersion heater and put the block into two containers. What's correct: Fundamentally flawed setup. Heater should be in a hole in the block (electrical method) or the block should be heated then moved to water (method of mixtures). Q=mcDT formula was also incorrect. Marks lost: 5 Reference: 62eb10cb-80c0-5f3c-ba90-00da26a78dff

Physics - Mechanics Describe the energy conversion when a student falls on a rubber mat and becomes stationary. My answer: Potential -> Kinetic -> transfers to the mat (to what form?) What's correct: Kinetic energy is converted into Internal energy (heat) and sound in the mat and student, and temporarily into elastic potential energy in the mat. Marks lost: 1 Reference: 694c6dbb-1523-540c-b5d5-8217135d925d

Physics - Mechanics Explain why the actual height of a jump is smaller than the calculated maximum height. My answer: There is air resistance, letting the whole velocity of the jump decreased. What's correct: Air resistance is a non-conservative force that does negative work, dissipating kinetic energy as thermal energy, so less GPE is gained. Marks lost: 1 Reference: 2aba5c12-17fd-5db0-938a-b167a36d50d6

Physics - Mechanics Find the angle of inclination theta using energy conservation and distance. My answer: theta = arccos(h/S) = 26.1 degrees. What's correct: Trigonometric error. Height h is opposite to the angle, so sin(theta) = h/S. Correct theta ≈ 63.8 degrees. Marks lost: 3 Reference: 8b19f510-7c53-545e-98df-23306415500b

Physics - Mechanics Find the initial speed of the block from an acceleration-time graph (linear decrease). My answer: u = -17.6 m/s (using v = u + at with a=8.8). What's correct: Since acceleration is not constant, change in velocity is the area under the a-t graph (trapezoid). Area = 12.6, so u = 12.6 m/s. Marks lost: 2 Reference: 4e7f8089-16d5-560e-aab0-77121442f364

Physics - Mechanics Draw a free body diagram for a block moving up a rough inclined plane. My answer: Included an 'applied force' pointing down the incline. What's correct: Only Normal force, Weight, and Kinetic Friction (pointing down the incline) should be shown. No additional applied force exists in the scenario. Marks lost: 1 Reference: 4e7f8089-16d5-560e-aab0-77121442f364

Physics - Mechanics Find the magnitude of force F and the normal force acting on a uniform rod in equilibrium. My answer: Used (1/2) for distance instead of 0.6m; Normal force = 25 N. What's correct: Calculations were numerically correct (F=25N, N=25N), but marks were lost due to ambiguous notation in the moment equation. Marks lost: 3 Reference: f41a7c30-b3e9-54a1-9edd-5752ab3940a0

Physics - Mechanics Describe and explain the motion of the boat after the oar is lifted from the water. My answer: The boat would remain at that point but it is vibrating. What's correct: By Newton's First Law (Inertia), the boat continues moving left, but resistive forces (drag) cause it to gradually slow down and eventually stop. Marks lost: 2 Reference: 54d96af2-9df9-53c8-8231-6ad441a40d36

Physics - Mechanics Explain why the boat moves left when the oar pushes water right. My answer: Water were pushed to the right side of the boat therefore...? What's correct: Incomplete explanation. Must state that water exerts an equal and opposite reaction force on the oar/boat towards the left (Newton's Third Law). Marks lost: 1 Reference: 54d96af2-9df9-53c8-8231-6ad441a40d36

Physics - Thermodynamics Explain features of a kettle that make it efficient for heating water on a stove. My answer: It has a high melting point. What's correct: A high melting point is a safety/functional requirement, not an efficiency feature. Correct features include metal's high thermal conductivity or a large base area for better heat transfer. Marks lost: 1 Reference: f7a8a4df-c2d3-5be7-8e22-ce666ea00894

Physics - Thermodynamics Calculate the mass of water vaporized during the final 5s of boiling. My answer: m = 9150 / (2.26 x 10^6) = 0.0162 kg What's correct: Numerical error. Correct mass m = Q/Lv = 9150 / 2.26e6 ≈ 0.00405 kg. Marks lost: 1 Reference: f7a8a4df-c2d3-5be7-8e22-ce666ea00894

Physics - Thermodynamics Calculate power output of a kettle by energy absorbed by water for temperature rise. My answer: Power = 78750 / 43 = 1830 W What's correct: Calculation was correct (1831 W), but marks were lost likely due to strict rounding or a marking error. Marks lost: 3 Reference: f7a8a4df-c2d3-5be7-8e22-ce666ea00894