A body takes 5 minute for cooling from 50⁰C to 40⁰C. Its temperature

⇦

⇨

A body takes 5 minute for cooling from 50⁰C to 40⁰C. Its temperature comes down to 33.33⁰C in next 5 minute. Temperature of surroundings is

Options

(a) 15⁰C
(b) 20⁰C
(c) 25⁰C
(d) 10⁰C

Correct Answer:

20⁰C

Explanation:

Apply Newton’s law of cooling
In first case, (50 – 40)/5 = K [(50+40)/2 – θ]
⇒ 2 = K [45 – θ] ——(i)
In second case, take 33.33 = 33 x (1/3) = 100/3
[40 – (100/3)]/5 = K {[40 + (100/3)/2] – θ}
⇒ 20/(5×3) = K [(110/3) – θ] ——(ii)
(i)/(ii) = (2 x 5 x 3)/20 = (45 – θ) / [(110/3) – θ]
⇒ 3/2 = (45 – θ) / [(110/3) – θ]
= 110 – 30 = 90 – 20 ⇒ θ = 20⁰C.

Related Questions:

1. A disc of moment of inertia (9.8/π²) kg m² is rotating at 600 rpm. If the frequency
2. When an input signal 1 is applied to a NOT gate, then its output is
3. The device can act as a complete electronic circuit is
4. Ohm’s law is not applicable except to
5. Transformer is used to

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