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. If the minimum energy of photons needed to produce photoelectrons is 3 eV,
2. A magnetic needle suspended parallel to a magnetic field requires √3J of work
3. If a mass of 20g having charge 3.0 mC moving with velocity 20ms⁻¹ enters a region
4. A balloon with mass m is descending down with an acceleration a
5. A stone falls freely under gravity. It covers distances h1, h2 and h3 in the first 5 secs

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