An electric drill rated 400W is used to drill a hole in copper of mass 400g in 20s. Calculate the rise in…

Analyze the question: A drill of known power runs for a known time, and all its energy becomes heat in the copper. We need the temperature rise.

Concept:

• Energy supplied: E = P × t
• Heat absorbed: Q = mcΔθ
• Since all the energy is absorbed, P × t = mcΔθ

Solution:

1. Energy produced: E = P × t = 400 W × 20 s = 8000 J

2. Convert the mass to kg: m = 400 g = 0.4 kg

3. Equate energy to heat absorbed: 8000 = 0.4 × 400 × Δθ 8000 = 160 × Δθ

4. Solve for Δθ: Δθ = 8000 ÷ 160 = 50 K (50 °C)

A temperature rise in kelvin equals the rise in °C, so the answer is 50 °C.

Tip: Always convert grams to kilograms before using Q = mcΔθ. Forgetting this is the most common mistake. If you had used 400 g directly, you would have gotten 0.05, which is not among the options. Also remember that Power × Time gives Energy (W × s = J).