A bowl filled with very hot soup cools from $98^{\circ} C$ to $86^{\circ} C$ in 2 minutes when the room temperature is $22^{\circ} C$. How long it will take to cool from $75^{\circ} C$ to $69^{\circ} C$ ?
A bowl filled with very hot soup cools from $98^{\circ} C$ to $86^{\circ} C$ in 2 minutes when the room temperature is $22^{\circ} C$. How long it will take to cool from $75^{\circ} C$ to $69^{\circ} C$ ?
- 2 minutes
- 1 minute
- $1.4$ minutes
- $0.5$ minute
The Correct Option is C
Solution and Explanation
\(\frac{Δ_Q}{Δ_t}=−K(T−T_0)\)
\(\frac{Δ_Q}{Δ_t}=−K(T_{avg}−T_0) \)
(i) \(\frac{ms×12}{2}=−K\;\bigg(\frac{98+86}{2}−22\bigg)\)
\(6=-\frac{K}{ms}\bigg[\frac{98+86}{2}−22\bigg] \)
\(6=−\frac{K}{ms}[70]\)….….. (i)
(ii) \(\frac{ms×6}{\triangle_t}=−K\bigg(\frac{75+69}{2}−22\bigg) \)
\(\frac{6}{Δ_t}=−\frac{K}{ms}(50)\).....(ii)
(ii) ÷ (i)
\(\frac{6}{Δ_t(6)}=\frac{70}{50} \)
\(Δ_t=\frac{7}{5}\)
=\(1.4\;min\)
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Concepts Used:
Thermal Properties of Matter
Anything that has mass or occupies space in the universe is commonly known as matter. There are five properties of matters namely chemical, mechanical, thermal, dimensional, and physical properties.
Read More: Thermal Properties of Matter
Heat Capacity:
The quantity of heat needed to change the temperature of the matter by 1° is known as the heat capacity of a material. The temperature is indicated in kelvin or Celsius and the amount of heat is shown in calories or joules. Specific heat capacity or molar heat capacity is used to calculate the heat capacity of the matter with the stated dimension.
Linear expansion is the situation when change takes place in one dimension or dimensional.
Thermal Expansion:
When heat is passed through the material, the change in the area, volume, and shape is recognized as the thermal expansion property of the material. The expansion of the railway tracks due to maximal heat which leads to accidents is an example of thermal expansion.
Thermal Conductivity:
This property is interconnected to the conductivity of heat. The amount of heat regulated by the material is directly proportional to the conductivity of the material. Not all objects have the capacity to conduct heat throughout their bodies. Insulators are such objects which do not have the property to conduct heat throughout their body.
Thermal Stress:
The stress due to thermal contraction or expansion of the body is known as thermal stress. The explosion of materials takes place due to thermal stress which is dangerous. The cracks on the truck tyres are caused by an outcome of thermal stress. Trucks at high speed generate heat which is caused by the friction of the truck tyres and the road surface.