JUPEB Physics
Past Questions

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## The reasoning Electric charge is a fundamental property of matter, like mass. Just as mass is measured in kilograms, **electric charge is measured in coulombs (C)**. Think of it this way: the coulomb is the "bucket" that holds charge. One coulomb represents approximately 6.24 × 10¹⁸ electrons worth of charge. This unit is named after French physicist Charles-Augustin de Coulomb. The relationship is simple: **Q = It**, where Q (charge in coulombs) = I (current in amperes) × t (time in seconds). So 1 coulomb = 1 ampere flowing for 1 second. ## Why the wrong options tempt you - **Volt** measures electric potential difference (how much "push" the charge has), not the charge itself - **Ampere** measures current (the *flow rate* of charge per second), not the amount of charge - **Ohm** measures resistance (opposition to current flow), totally different concept These all relate to electricity, so they sound plausible if you're rushing! ## Quick takeaway **Coulomb counts the charge; ampere counts how fast it flows; volt counts the push; ohm counts the resistance.** Remember: C for Charge = Coulomb!

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Work = force × distance; SI unit is joule (J) = N·m.

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Newton's first law (inertia): an object preserves its state of motion unless a net force acts on it.

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g ≈ 9.8 m/s² (often approximated as 10 m/s² in calculations).

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Frequency = cycles per second. SI unit = hertz (Hz) = 1/s.

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Sound is a longitudinal mechanical wave — particles oscillate in the direction of wave travel.

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V = IR = 2 × 10 = 20 V.

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Convex (converging) lenses focus parallel light to a point. Concave lenses diverge light.

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Violet has highest frequency / shortest wavelength in the visible spectrum. Red is the opposite extreme.

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KE = ½ × mass × velocity² (energy of motion). mgh = potential energy due to height.

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The net force is $20 - 5 = 15$ N, so $a = \dfrac{F_{net}}{m} = \dfrac{15}{3} = 5$ m s$^{-2}$. Using the applied force alone gives $6.67$ m s$^{-2}$, and adding friction instead of subtracting gives $8.33$.

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At maximum height $v = 0$, so from $v^2 = u^2 - 2gh$: $0 = 900 - 20h$, giving $h = 45$ m. Forgetting the factor 2 in $2gh$ gives 90 m.

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Time of flight $T = \dfrac{2u\sin\theta}{g} = \dfrac{2 \times 20 \times \sin 30^\circ}{10} = \dfrac{2 \times 20 \times 0.5}{10} = 2$ s. Using $\cos 30^\circ$ gives $2\sqrt{3}$, and omitting the factor 2 gives the time to maximum height, 1 s.

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By conservation of momentum, $2 \times 6 + 4 \times 0 = (2 + 4)v$, so $12 = 6v$ and $v = 2$ m s$^{-1}$. Dividing the momentum by the mass of the second trolley only gives 3 m s$^{-1}$.

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Impulse equals change in momentum: $Ft = mv - 0$, so $50 \times 0.2 = 0.5v$, giving $v = \dfrac{10}{0.5} = 20$ m s$^{-1}$. Stopping at the impulse of 10 N s and reporting it as velocity is the usual error.

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From $h = \dfrac{1}{2}gt^2$: $45 = 5t^2$, so $t^2 = 9$ and $t = 3$ s. Dividing height by $g$ gives $4.5$, which has the wrong units and ignores the square.

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Range $R = \dfrac{u^2\sin 2\theta}{g} = \dfrac{400 \times \sin 60^\circ}{10} = 40 \times \dfrac{\sqrt{3}}{2} = 20\sqrt{3} \approx 34.6$ m. Using $\sin\theta$ instead of $\sin 2\theta$ gives 20 m.

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Displacement is the area under the velocity-time graph, a trapezium: $\dfrac{4 + 10}{2} \times 3 = 21$ m. Using the final velocity alone gives 30 m; using only the change in velocity gives 18 m.

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The scale reads the normal reaction $N$. From $N - mg = ma$: $N = m(g + a) = 60 \times 12 = 720$ N. A reading of 480 N would apply if the lift were accelerating downwards, and 600 N is the true weight, read only when the lift is not accelerating.