When a cast-iron bar is heated by 3 degrees, its internal energy has increased by 1296 J. Find the mass of the bar.

Initial data: Δt (change in the temperature of the cast iron bar) = 3 ºС; Q (the amount by which the internal energy of the bar has increased) = 1296 J.

Reference data: C (specific heat capacity of cast iron) = 540 J / (kg * K).

We express the mass of a cast-iron bar from the following formula: Q = C * m * Δt.

m = Q / (C * Δt).

Let’s do the calculation:

m = 1296 / (540 * 3) = 0.8 kg or 800 g.

Answer: The mass of a cast iron bar is 800 grams.