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. A light of wavelength 5000Å falls on a sensitive plate with photoelectric work
2. Two closed pipes produce 10 beats per second when emitting their fundamental nodes.
3. If the self inductance of 500 turn coil is 125 mH, then the self inductance
4. The workdone in turning a magnet of magnetic moment M by an angle of 90⁰ from the magnetic
5. A beaker of radius 1.5 cm is filled with a liquid of surface tension 0.075 N/m

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