JAMB Physics 2009
Questions & Answers

Students might mistakenly choose velocity, force, or work because all are common mechanics terms used in physics problems. Mass is a fundamental physical quantity measured in kilograms because it stands independent, whereas velocity, force, and work are derived quantities computed from base units. Common mistake: confusing derived quantities with fundamental base units.

Students might select 230 kmh⁻¹ by incorrectly adding the two speeds together as if the cars were traveling toward each other. Since both vehicles move in the same direction, relative velocity requires finding the difference between their speeds, yielding 130 kmh⁻¹ minus 100 kmh⁻¹, which equals 30 kmh⁻¹. Common mistake: adding relative speeds instead of subtracting them when objects move in the same direction.

Students might choose constant speed or deceleration by misreading the directional slant of graph lines. The positive slope located between points F and G on the velocity-time graph clearly indicates that the car accelerates. Common mistake: misinterpreting positive slopes on velocity-time graphs as constant motion.

Students might choose the stone will reach the ground first, assuming heavier objects naturally fall faster in everyday environments. When air resistance is ignored, all objects fall at the exact same rate regardless of mass, meaning both will reach the ground simultaneously. Common mistake: letting everyday air resistance bias free-fall physics principles.

Students might mistakenly choose option B (25 ms⁳ ) by confusing the initial velocity with the final acceleration value or option A (5 ms⁳ ) through miscalculation. To find the acceleration, determine the change in velocity by subtracting the initial velocity (25 ms⁳ ) from the final velocity (45 ms⁳ ), which gives 20 ms⁳ . Then, divide this difference by the given time of 10 s, yielding 2 ms⁳ . Common mistake: Forgetting to divide the velocity change by the time interval.

A student might select option A or B by assuming mass and weight change together or that mass is what varies with location. Because mass is an intrinsic property, it remains constant no matter where it is measured, whereas weight depends directly on the gravitational field strength at different locations. Common mistake: Confusing the invariable nature of mass with the location-dependent nature of weight.

A student might pick option B or D by confusing peaks with troughs on the undulating surface. Stable equilibrium is found at the lowest points where a displaced ball will naturally return to rest, corresponding to positions II, V, and VIII. Common mistake: Selecting unstable equilibrium points (peaks) instead of stable ones (troughs).

A student might accidentally choose option A (0.250 J) by omitting the cosine term or using incorrect subtraction. The work done by the variable horizontal force is equal to the weight multiplied by the vertical displacement, calculated as 0.1 multiplied by 0.5 multiplied by (1 minus cos 60°). Since cos 60° is 0.5, this simplifies to 0.1 × 0.5 × 0.5, which results in 0.050 J. Common mistake: Failing to subtract cos 60° from one when calculating the vertical height change.

Options like B, C, or D might look plausible if a student associates conveyor robustness with general durability rather than traction. Conveyor belt surfaces are built rough to increase friction, which successfully prevents the load from slipping during transport. Common mistake: Assuming structural strength is the primary reason for texture modifications in transport systems.

A student might select option A or B due to incorrect handling of the mechanical advantage formula. Efficiency is determined by dividing the mechanical advantage by the velocity ratio and multiplying by 100. First, find the mechanical advantage as 800 divided by 400 (which is 2), then divide by the velocity ratio of 6, and finally multiply by 100 to get 33.3%. Common mistake: Inverting the mechanical advantage and velocity ratio in the percentage calculation.

A student might choose option A or C by improperly converting the length extension from centimeters to meters or misapplying the force value. Strain energy is calculated as 0.5 multiplied by the force and the extension. Using an extension of 0.005 m (derived from 30.5 cm minus 30 cm) and a force of 300 N, the energy evaluates to 0.5 × 300 × 0.005, giving 0.75 J. Common mistake: Using 0.5 cm directly as the extension without converting it to meters.

Options like B or C might be chosen if a student mixes up the values for pressure and area. The force exerted on the second piston is found by multiplying the pressure by the cross-sectional area, which is 100 Pa multiplied by 3 m², yielding a total of 300 N. Common mistake: Dividing the area by pressure instead of multiplying them.

Students might mistakenly pick a eureka can or pipette thinking they measure powder volume. An accurate measurement of the relative density of a substance in its powdered form is uniquely accomplished using a density bottle. Common mistake: Confusing general liquid measuring glassware with specialized density measurement apparatus.

A student might pick option C or D by confusing fluid density with humidity or vapor pressure. A hydrometer is an instrument utilized for measuring the relative density of a liquid by comparing its density to that of water. Common mistake: Mistaking relative density measurement for atmospheric or vapor properties.

Options like B, C, or D might seem appealing if a student misunderstands temperature ranges. Alcohol possesses a low freezing point, which allows it to remain liquid at much lower temperatures, making it a superior choice for cold environments compared to mercury. Common mistake: Assuming a lower boiling point rather than a lower freezing point is what helps in cold conditions.

A student might select option A or D by adding or subtracting the ratios instead of multiplying them. The increase in length is proportional to the product of expansivity and length. Therefore, the ratio of increase is found by multiplying the expansivity ratio (2/3) by the length ratio (3/4), which simplifies to 1/2, meaning the ratio for P to Q is 2:1. Common mistake: Adding the given ratios instead of multiplying them together.

Options B or D might be selected if a student multiplies the values or uses an incorrect formula. Density is calculated by dividing mass by volume, which in this case is 4000 kg divided by 5 m³, resulting in 800 kgm⁳⁵. Common mistake: Multiplying mass and volume instead of dividing mass by volume.

A student might choose option A or B by assuming all heat or light comes directly from the sun or visible spectrum. Hot objects emit heat primarily as infrared rays, which are a specific form of electromagnetic radiation. Common mistake: Equating thermal radiation exclusively with visible light or solar energy.

A student might mistakenly think the level drops or overflows (options A or D) because ice has a larger volume than liquid water. However, floating ice displaces a weight of water exactly equal to its own weight; when the ice completely melts, the water level remains unchanged. Common mistake: Overlooking Archimedes' principle regarding floating bodies and assuming melting ice changes the container fluid level.

Options like B or C might be chosen if a student confuses ground-level condensation with suspended atmospheric moisture. Dew refers to the small droplets of water that form on cool surfaces like grass overnight when water vapor condenses. Common mistake: Confusing dew (surface condensation) with mist or fog (suspended vapor).