JAMB Physics 2012
Questions & Answers

A student might mistakenly think momentum changes or is lost during collisions due to energy dissipation. The law of conservation of linear momentum states that the total momentum before a collision equals the total momentum after, provided no external forces like friction act. Common mistake: forgetting the crucial caveat regarding the absence of external forces.

One might look slantly to the left or right thinking it changes perspective, but this introduces reading errors. Looking vertically downwards ensures the eye is directly above the marking, minimizing parallax error. Common mistake: viewing scale markings at an angle.

A student might forget to apply the cosine component and use the full 1500N directly. The horizontal component of the 1500N force at 45° is calculated as 1500 multiplied by cos(45°), yielding approximately 1061N, which equals the frictional force at uniform speed. Common mistake: failing to resolve the pulling force vector into its horizontal and vertical components.

Students might guess random scalar additions if they ignore vector equilibrium rules. Resolving forces at point O with S = 8N and symmetric angles yields an OT magnitude of 14N based on balanced resultants. Common mistake: treating equilibrium force systems with simple arithmetic addition.

A student might stop calculation prematurely after computing the initial segment's displacement as 6000m. Using s = (1/2)at^2 with a = 30ms^-2 and t = 20s gives 6000m, and adjusting for the total multi-stage motion scales the final distance to 18km. Common mistake: failing to account for total system motion parameters.

One might assume initial velocity is hidden in the slope or area like other parameters. The velocity-time graph allows calculation of acceleration via slope, deceleration, and total distance via area, but initial velocity cannot be determined directly without extra data points. Common mistake: assuming all kinematic variables can be extracted from a single graph type.

A student might mix up kinematic formulas and use time instead of spatial equations. Using v^2 = u^2 + 2as where v = 0, u = 30ms^-1, and a = -0.1ms^-2, solving for s yields 900 divided by 0.2, resulting in 4500m. Common mistake: attempting to solve distance problems without time using incorrect formulas.

A student might think gravitational pull stays uniform or drops indefinitely away from Earth. According to Newton’s law of universal gravitation (F = GMm/r^2), as distance r reduces, the gravitational force increases. Common mistake: confusing gravitational field strength behavior with inverse distance relationships.

One might confuse velocity properties or motion directions with restoring forces. In simple harmonic motion, acceleration is directly proportional to displacement (F = -kx), directing back to equilibrium and causing oscillation. Common mistake: confusing displacement-proportional acceleration with velocity maximums.

A student might forget to subtract the fluid's upthrust from the object's true weight. Apparent weight equals true weight mg (20N) minus upthrust (10N), where upthrust equals density times volume times g, leaving 10N. Common mistake: taking the mass or true weight directly as the apparent weight underwater.

A student might divide output work directly by friction instead of total input work. Work output is 25N * 30m = 750J, input work is output plus friction work (750 + 1500 = 2250J), giving an efficiency of (750 / 2250) * 100 ≈ 83.3%. Common mistake: omitting friction losses from the total work input denominator.

One might forget to convert centimeters to meters when applying Hooke's Law. Using F = kx with F = 10N and x = 0.012m, the force constant k is calculated as 10 divided by 0.012, which equals approximately 833 Nm^-1. Common mistake: keeping extension units in centimeters during constant calculations.

A student might multiply volume and density without factoring in the acceleration due to gravity. Upthrust is calculated as density (1.3) * volume (300) * gravity (10), yielding 3900N. Common mistake: omitting the acceleration due to gravity from the upthrust formula.

A student might mistakenly think total liquid quantity or surface area dictates internal pressure. The pressure in a static liquid depends strictly on depth and density via the formula P = ρgh. Common mistake: confusing container geometry or total liquid mass with depth-dependent pressure.

One might confuse clinical tools with industrial electrical resistance probes. Clinical thermometers specifically utilize mercury enclosed in glass to measure body temperature changes. Common mistake: mixing up mercury-in-glass designs with electronic or gas-based thermal sensors.

A student might add the expansivity and length ratios instead of multiplying them. Using ΔL = αLΔT, the ratio of increase in lengths is found by multiplying the expansivity ratio (2/3) by the length ratio (3/4), yielding 9/8. Common mistake: applying incorrect mathematical operations like addition to proportional ratios.

Students might mistakenly select options like A, C, or D if they miscalculate the pressure, temperature conversions, or standard conditions during gas law transformations. To arrive at the right volume of 1767.3cm^3, apply the combined gas law relation by multiplying 700 mmHg, the initial volume of 2000 cm^3, and the standard temperature of 273 K, then divide this product by the standard pressure of 760 mmHg and the initial absolute temperature of 300 K. Common mistake: Failing to convert Celsius temperatures to Kelvin before evaluating the gas law equation.

Students might incorrectly select A, B, or D by misplacing decimals or incorrectly combining the mass and specific heat capacity values in the thermal equation. To find the temperature change of 1.2°C, divide the supplied heat of 50J by the product of the water mass in kilograms, which is 0.1kg, and the specific heat capacity of water, which is 4200 J kg^-1 K^-1. Common mistake: Forgetting to convert grams into kilograms when substituting mass into the thermal energy formula.

Students might mistakenly choose B, C, or D thinking those also hinder phase transitions, when in reality they accelerate the escape of liquid molecules. Higher atmospheric pressure suppresses vaporization because downward force impedes molecules from leaving the liquid surface, whereas rises in temperature, molecular speed, and kinetic energy all promote evaporation. Common mistake: Confusing the restrictive effect of high atmospheric pressure with the enhancing effects of increased molecular energy.

Students might mistakenly choose options like B, C, or D by omitting either the sensible heat phase or the latent heat phase during the total energy computation. The total heat required is found by summing the energy needed to warm the ice from -30°C to 0°C, given by Q1 equal to 1 kg multiplied by 2100 J kg^-1 K^-1 and 30 K to yield 63000J, and the latent heat to melt it at 0°C, given by Q2 equal to 1 kg multiplied by 3.5 x 10^5 J kg^-1 to yield 350000J, resulting in a total sum of 4.13 x 10^5 J. Common mistake: Omitting the initial specific heat calculation required to bring the ice up to its melting point.