Correct Answer: A

Rationale: The velocity of a wave can be determined by multiplying the frequency of the wave by the wavelength. This relationship is given by the formula: velocity = frequency wavelength. By multiplying the frequency by the wavelength, you can calculate the speed at which the wave is traveling. This formula is derived from the basic wave equation v = f λ, where v represents velocity, f is frequency, and λ is wavelength.
Therefore, to find the velocity of a wave, one must multiply its frequency by its wavelength.

Choices B, C, and D are incorrect. Adding, subtracting, or dividing the frequency and wavelength does not yield the correct calculation for wave velocity. The correct formula for determining wave velocity is to multiply the frequency by the wavelength.

Correct Answer: D

Rationale: Work done is calculated using the formula: Work = Force x Distance. In this case, the force applied is 15 N and the distance covered is 3 m. Thus, work done = 15 N x 3 m = 45 Nâ‹…m.
Therefore, the correct answer is 45 Nâ‹…m.
Choice A (5 W) is incorrect because work is measured in joules (J) or newton-meters (Nâ‹…m), not in watts (W).
Choice B (5 Nâ‹…m) is incorrect as it miscalculates the work by not multiplying the force by the distance.
Choice C (45 W) is incorrect because work is not measured in watts (W) but in newton-meters (Nâ‹…m).

Correct Answer: B

Rationale: When a hot cup of coffee is placed on a cold table, heat transfer primarily occurs through conduction. Conduction is the process of heat transfer through direct contact between objects at different temperatures. In this scenario, the heat from the hot coffee cup is transferred to the cold table through direct contact, making conduction the primary mode of heat transfer.
Choice A (Radiation) is incorrect because radiation is the transfer of heat through electromagnetic waves, which is not the primary mode of heat transfer in this scenario.
Choice C (Convection within the coffee) is incorrect because convection is the transfer of heat through the movement of fluids, which is not the primary mode of heat transfer in this scenario.
Choice D (A combination of conduction and convection) is incorrect because while convection may play a minor role due to air currents around the cup, the primary mode of heat transfer in this scenario is conduction.

Correct Answer: A

Rationale:
To find the magnitude of the resulting force between two charges, we can use Coulomb's law, which states that the force is directly proportional to the product of the charges and inversely proportional to the square of the distance between them. The formula for Coulomb's law is:
F = k (|q1 q2| / r²),
where F is the force, k is the Coulomb constant, q1 and q2 are the charges, and r is the distance between the charges. Substituting the given values into the formula:
F = (9 10⁹ N·m²/C²) ((4 10⁻⁶
C) (2 10⁻⁶
C) / (1 m)²) = 0.04 N.

Therefore, the magnitude of the resulting force between the objects is 0.04 N.

Correct Answer: C

Rationale: When the heat of a reaction is negative, it indicates that the reaction releases energy in the form of heat. This means that the products have lower energy levels compared to the reactants. Lower energy levels are associated with greater stability in chemical systems.
Therefore, when the heat of a reaction is negative, the products are more stable due to having less energy than the reactants.
Choice A, stating that the products have less energy and are less stable, is incorrect as lower energy levels imply greater stability.
Choice B, stating that the products have more energy and are more stable, is incorrect as lower energy levels lead to higher stability.
Choice D, stating that the products have more energy and are less stable, is incorrect as lower energy levels are associated with higher stability.