Two kilograms of solids X and Y at 10°C each absorb 5 joules of heat energy. The final temperatures of X and Y are 15°C and 20°C, respectively. Compared to X, Y must have a lower ...?

• A. Specific heat
• B. Density
• C. Melting point
• D. Thermal conductivity

Answer: (A)

The key idea is how much energy is needed to raise the temperature of a material per unit mass. The relation Q = m c ΔT links heat input, mass, specific heat, and temperature rise.

Both X and Y have the same mass and receive the same heat energy. Their temperature increases are different: X rises by 5°C, Y rises by 10°C. Using c = Q/(m ΔT):

• For X: c = 5 J / (2 kg × 5°C) = 0.5 J/(kg·°C)

• For Y: c = 5 J / (2 kg × 10°C) = 0.25 J/(kg·°C)

Since Y experiences a larger temperature rise for the same heat input, it has a lower specific heat than X. The other properties listed (density, melting point, thermal conductivity) do not directly determine how much a given amount of heat will raise the temperature of a substance in this setup, so they aren’t what’s being compared here.