JAMB Physics 2017 Past Questions & Answers

The question requires identifying the incorrect equation of motion. The three standard equations for uniform acceleration are v = u + at, s = ut + ½at², and v² = u² + 2as. Options B and C are standard forms, while option D is a direct rearrangement of v² = u² + 2as. Option A, a = (v² − u²)/2, is incorrect because the correct rearrangement to find 'a' is a = (v² − u²)/2s; it is missing the distance 's' in the denominator.

Common mistake: Students might hastily choose option D, thinking that a rearranged formula is different from the original, but it is just another valid form of the equation v² = u² + 2as.

Electromagnetic waves, such as X-rays, radio waves, and sunlight, are created by vibrating electric and magnetic fields and can travel through a vacuum (empty space). Sound waves, however, are mechanical waves which need a medium like air, water, or solids to travel by causing vibrations in the particles of that medium. Because sound waves require a medium and are not electromagnetic in nature, they are not a form of electromagnetic radiation.

Common mistake: A common mistake is choosing sunlight because students might think of it only as visible light, not realizing it is a broad spectrum of electromagnetic radiation including ultraviolet and infrared waves.

To find the electric field intensity (E) between two plates, you use the formula E = V/d, where V is the potential difference and d is the distance between them. First, you must convert the distance from centimeters to meters by dividing by 100, so 35cm becomes 0.35m. Then, substitute the values into the formula: E = 6.5V / 0.35m, which gives an answer of 18.57 NC⁻¹.

Common mistake: The most common mistake is forgetting to convert the distance from centimeters (cm) to the standard unit of meters (m) before performing the calculation.

Every bridge has a natural frequency at which it vibrates easily, similar to a guitar string. When soldiers march in step, they apply a periodic force to the bridge with a specific frequency. If this marching frequency matches the bridge's natural frequency, resonance occurs, causing the bridge's vibrations to grow dangerously large and potentially lead to its collapse. By marching disorderly, they break this regular rhythm and prevent resonance from happening.

Common mistake: Students often mistakenly choose option D, thinking the issue is about evenly distributing the soldiers' weight, but the key concept is avoiding the dynamic effect of resonance caused by rhythmic marching.

This question requires the application of Archimedes' principle, which states that the upthrust on a submerged object is equal to the weight of the fluid it displaces. The formula is Upthrust = Volume × Density × g. First, convert the volume from 50 cm³ to the standard unit of m³ by multiplying by 10⁻⁶, which gives 50 x 10⁻⁶ m³. Then, calculate the upthrust: (50 x 10⁻⁶ m³) × (10³ kgm⁻³) × (10 ms⁻²) = 0.5 N.

Common mistake: Students often forget to convert the volume from cubic centimeters (cm³) to cubic meters (m³) before performing the calculation, leading to an incorrect answer.

A discharge tube contains a gas at a very low pressure. To produce cathode rays, a high voltage is applied across the tube. The low pressure ensures there are few gas molecules to obstruct the path of the electrons. The high voltage provides a strong electric field, which pulls electrons from the negative terminal (cathode) and accelerates them towards the positive terminal (anode), forming the cathode rays.

Common mistake: Students often correctly remember that high voltage is needed but might mistakenly choose 'high pressure', forgetting that a high pressure would mean too many gas molecules are present, which would prevent the electrons from travelling freely across the tube.

In Physics, work is done only when a force causes an object to move a certain distance in the direction of that force. When the boy climbs onto the table, he applies an upward force to lift his body weight, and he moves a vertical distance. Because there is both a force and a displacement, work is done.

Common mistake: Students often confuse the everyday meaning of 'work' (which involves effort) with the strict physics definition, leading them to pick option A because supporting a heavy load feels tiring, even though no distance is moved.

The relationship between heat energy (Q), mass (m), and specific latent heat (L) during a change of state is given by the formula Q = mL. To find the specific latent heat of vaporization (L), we rearrange the formula to L = Q / m. Substituting the given values, we have L = $(1.13 × 10⁶ J)$ / 15 kg. This calculation gives us 75333.3 J/kg, which is written in standard form as 7.53 × 10⁴ Jkg⁻¹.

Common mistake: Students often make a mistake by incorrectly handling the scientific notation after dividing, leading them to choose option B by misplacing the decimal point.

The efficiency of a cell is the ratio of the power delivered to the external resistor (the useful output) to the total power supplied by the cell. This can be calculated using the formula: Efficiency = [R / (R + r)] x 100%, where R is the external resistance and r is the internal resistance. Substituting the given values, we get Efficiency = [6Ω / (6Ω + 2Ω)] x 100%, which simplifies to $(6/8)$ x 100% or 75.00%.

Common mistake: Students might mistakenly calculate the percentage of energy wasted inside the cell, which is [r / (R + r)] or $(2/8)$, leading them to choose 25.00%.

According to the kinetic theory of matter, all matter is composed of tiny molecules that are in a state of continuous, random motion. In liquids, these molecules are not stationary but constantly move and slide past one another, which is why liquids can flow. Temperature is the measure of the average kinetic energy of these moving molecules, so for molecules to be stationary (as option A suggests) is incorrect.

Common mistake: A student might mistakenly choose option D, thinking that molecules in solids are completely stationary, not realizing that even in solids, molecules are constantly vibrating in fixed positions.