A body of mass 40g loses 80J of heat energy. If the specific heat capacity of the body is 400 Jkg-1, calculate the change in temperature of the body.

Analyze the question: We're given the mass, the heat lost, and the specific heat capacity, and we need the temperature change. (The unit of specific heat capacity should be J kg⁻¹ K⁻¹, so the question has a small typo.)

Concept: The heat gained or lost by a body is

Q = mcΔθ

so

Δθ = Q / (mc)

Solution:

• Mass: m = 40 g = 0.04 kg (always convert grams to kilograms)
• Heat lost: Q = 80 J
• Specific heat capacity: c = 400 J kg⁻¹ K⁻¹

Δθ = 80 / (0.04 × 400)

Δθ = 80 / 16

Δθ = 5.0 K

The body loses heat, so its temperature falls by 5.0 K. The question asks for the magnitude of the change, which is 5.0 K.

Answer: Option D, 5.0 K.

Tip: Check the units before you substitute. Mass must be in kg for the formula to work. If you had used 40 g directly, you would have got 0.005, which is not among the options. Also, 0.04 × 400 = 16 is a quick mental calculation, and 80 ÷ 16 = 5.