Certain quantity of water cools from 70⁰ C to 60⁰C in the first 5 minutes and to 54⁰C

⇦

⇨

Certain quantity of water cools from 70⁰ C to 60⁰C in the first 5 minutes and to 54⁰ C in the next 5 minutes. The temperature of the surroundings is

Options

(a) 45⁰ C
(b) 20⁰ C
(c) 42⁰ C
(d) 10⁰ C

Correct Answer:

45⁰ C

Explanation:

Let the temperature of surroundings be θ₀
By Newton’s law of cooling
(θ₁ – θ₂ / t) = k [(θ₁ – θ₂ / 2) – θ₀]
[(70 – 60) / 5] = k [(70 + 60 / 2) – θ₀] ⇒ 2 = k [65 – θ₀] ——(i)
Similarly, (60 – 54) / 5 = k = [(60 + 54 / 2) – θ₀]
6 / 5 = k [57 – θ₀] ——–(ii)
By dividing (i) by (ii) we have
10 / 6 = (65 – θ₀) / (57 – θ₀) ⇒ θ₀ = 45⁰

Related Questions:

1. Two liquid drops having diameters of 1 cm and 1.5 cm. The ratio of excess
2. An ideal gas is compressed to half its initial volume by means of several processes.
3. The self-inductance of a choke coil is 10 mH. When it is connected with a 10 V DC source,
4. Two equal and opposite charges of masses m₁ and m₂ are accelerated
5. The friction of the air causes a vertical retardation equal to 10%

Topics: Properties of Bulk Matter (130)
Subject: Physics (2479)

---

Important MCQs Based on Medical Entrance Examinations To Improve Your NEET Score

18000+ students are using NEETLab to improve their score. What about you?

Solve Previous Year MCQs, Mock Tests, Topicwise Practice Tests, Identify Weak Topics, Formula Flash cards and much more is available in NEETLab Android App to improve your NEET score.

---

Share this page with your friends