JAMB Physics 2002
Questions & Answers

Options such as temperature, speed, and energy might be selected if a student fails to remember the distinction between scalar and vector measurements. Velocity is uniquely correct because it encompasses both magnitude and direction, whereas the other choices are strictly scalars. Common mistake: Forgetting that speed has only magnitude while velocity includes direction.

A student might pick option A or D through arithmetic errors when rearranging the kinematic equation or neglecting the square root step. By applying the equation s = ut + (1/2)gt^2 where initial velocity u is 0, distance s is 45 m, and acceleration g is 10 ms^-2, we substitute to get 45 = 5t^2. Simplifying yields t^2 = 9, which evaluates to a time of t = 3 s, making option B the right choice. Common mistake: Forgetting to take the square root of t^2 when solving for time.

A student might select option A or B by dividing the force and time instead of multiplying them together. The correct answer is C because change in momentum is calculated by multiplying the applied force by the time interval, resulting in 10 multiplied by 4, giving 40 kgms^-1. Common mistake: Dividing force by time instead of multiplying them to find momentum change.

Students could mistakenly select option D by simply taking the total launch velocity without factoring in the angle. The correct choice is C because the horizontal component is determined by multiplying the velocity v by the cosine of 30°, which is 20 multiplied by the square root of 3 over 2, approximating to 17.3 ms^-1. Common mistake: Using the full velocity magnitude for the horizontal component without applying the cosine function.

Option A might be incorrectly chosen if the velocity is not squared in the formula. Option D is correct because kinetic energy is found using (1/2)mv^2, which translates to one-half times 5 kg times the square of 8 ms^-1, leading to 320 J. Common mistake: Forgetting to square the velocity term in the kinetic energy equation.

Option A or B might be chosen if the load and effort values are inverted or subtracted. Option C is correct because mechanical advantage is determined by dividing the load by the effort, which is 600 N divided by 200 N, yielding 3. Common mistake: Inverting the ratio by dividing effort by load.

Options B, C, or D might look plausible if a student confuses material properties with aerodynamic principles. Option A is correct because helium possesses a lower density than surrounding air, which creates the buoyant force necessary to make the balloon rise. Common mistake: Attributing buoyancy to chemical reactivity rather than density differences.

A student might select option B or C by miscalculating the product of gravity and depth in the denominator. Option A is correct because rearranging the pressure formula P = ρgh gives density ρ equal to pressure divided by the product of g and h, which is 5000 divided by 10 times 2, resulting in 250 kgm^-3. Common mistake: Multiplying the pressure by depth and gravity instead of dividing.

Option B might be picked by mistakenly assuming that pressure decreases when volume is reduced. Option A is correct because Boyle's law states that P1V1 equals P2V2 at constant temperature, meaning when the volume is cut in half, the pressure must double to compensate. Common mistake: Assuming an inverse relationship means pressure decreases when volume decreases.

Option A or B might be chosen by failing to multiply the linear expansivity by 3 to find the cubical expansivity. Option C is correct because the volumetric expansivity gamma is three times the linear expansivity alpha (6 × 10^-5 K^-1), the initial volume is the cube of 0.1 m (0.001 m^3), and the volume increase is found using ΔV = VγΔT, yielding 3.6 × 10^-4 m^3. Common mistake: Using linear expansivity directly instead of cubical expansivity for volume expansion.

A student might choose option A or C by improperly grouping the mass and temperature change in the denominator. Option B is correct because the specific heat capacity formula c = Q / (mΔT) evaluates to 1500 divided by the product of 0.5 kg and 5°C, resulting in 600 Jkg^-1K^-1. Common mistake: Multiplying energy by mass and temperature change instead of dividing.

Option A might be selected by confusing the behavior of boiling points under pressure with freezing points. Option B is correct because lower ambient pressure reduces the thermal energy required for liquid molecules to escape into the gas phase, thereby decreasing the boiling point. Common mistake: Confusing the effects of increased versus decreased pressure on boiling points.

Option A or C could be selected if frequency and velocity are multiplied or inverted improperly. Option B is correct because wavelength is calculated by dividing wave speed by frequency, which is 300 ms^-1 divided by 600 Hz, giving 0.5 m. Common mistake: Multiplying speed by frequency instead of dividing speed by frequency.

A student might pick option A by adding a flat numerical difference instead of scaling proportionally with the square root of absolute temperature. Option B is correct because sound speed is proportional to the square root of the absolute temperature in Kelvin, giving a ratio of the square root of 313 over 293 multiplied by 343 ms^-1, which equals approximately 355 ms^-1. Common mistake: Using Celsius temperatures directly in speed ratios without converting to Kelvin.

Option A or C might be mistakenly calculated by treating the pipe as open-ended instead of closed at one end. Option B is correct because the fundamental frequency of a pipe closed at one end is given by f = v / (4L), which means 170 equals 340 divided by 4L, simplifying to 4L = 2 and thus a length L of 0.50 m. Common mistake: Using the formula for an open pipe (v / 2L) instead of a closed pipe (v / 4L).

Options A, B, or C might be chosen if a student confuses wave-like properties of light with its corpuscular behavior. Option D is correct because the photoelectric effect specifically illustrates light acting as discrete packets or photons that eject electrons, proving its particle nature. Common mistake: Confusing wave interference phenomena with the quantum particle nature demonstrated by electron ejection.

Option A might be selected if the image distance is miscalculated as virtual. Option B is correct because applying the mirror formula 1/f = 1/u + 1/v with f = 15 cm and u = 20 cm yields 1/v = 1/60, resulting in v = 60 cm, and because the object is placed beyond the focal point, the formed image is real and inverted. Common mistake: Assuming all concave mirror images are virtual regardless of object position.

Option B or C could be chosen by using incorrect refractive index formulas or forgetting the apex angle. Option A is correct because the angle of minimum deviation for a prism is calculated as delta_m = (n - 1)A, which is (1.5 - 1) multiplied by the 60° apex angle, resulting in 30°. Common mistake: Forgetting to subtract one from the refractive index before multiplying by the apex angle.

Option A or B might be chosen if the sine component of the angle is omitted from the magnetic force equation. Option C is correct because rearranging F = qvB sin(60°) gives B equal to the force divided by qv times sin(60°), which evaluates to 3 × 10^-3 divided by 2 × 10^-6 times 5 times 0.866, yielding 0.4 T. Common mistake: Forgetting the angular sine term when calculating magnetic force on a moving charge.

Option A or C might be selected through simple arithmetic multiplication errors with the current and length. Option B is correct because the magnetic force on a current-carrying wire is F = BIL sin(90°), which multiplies 0.5 T by 2 A by 0.1 m by 1, resulting in 0.10 N. Common mistake: Incorrectly placing decimal points when multiplying small decimal values for magnetic field and length.