Thermal Properties of Matter Test

Result

Thermal Properties of Matter Test - 51

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Question 1
1 / -0

A lead bullet, of initial temperature $$27 ^ { \circ } C$$ and speed $$'v'$$ kmph pnetrates into a solid object and melts. If $$50\%$$ of the kinetic energy is used to heat it, The value of $$V$$ is kmph is (for leads melting point = 600 K, latent heat of fusion = $$2.5 \times 10 ^ { 4 } J$$ $$\mathrm { Kg } ^ { - 1 }$$ : specific heat = $$125 J$$ $$k g ^ { - 1 } K ^ { - 1 }$$

A
1800

B
3600

C
1200

D
1000

Solution
Question 2
1 / -0

If water at $$0^0C$$, kept in a container with an open top, is placed in a large evacuated chamber,

A
all the water will freeze

B
all the water will vaporize

C
part of the water will vaporize and the rest will freeze

D
ice, water and water vapour will be formed and reach equilibrium at the triple point

Solution
Question 3
1 / -0

A body at $$50^{0}C$$ cools in a surrounding maintained at $$30^{0}C$$. The temperature at which the rate of cooling is half that of beginning is:

A
$$16.32^{0}C$$

B
$$26.3^{0}C$$

C
$$40^{0}C$$

D
$$46.3^{0}C$$

Solution

The rate of cooting $$(R)$$ of a body from Newton's Law of cooting is:-
$$R=\dfrac {dt}{dx}=-k(T-T_0)\quad T:$$ temp of body at time $$t$$
and $$T_0:$$ Surrounding $$r$$ temp
Given initially $$T=30^oC$$ and rate in $$R$$
when temp drops to half $$(R'=R/2)$$ then temp of body be $$T'$$.
so, we have:-
$$R=-4(50^oC-30^oC)=-20k\ ^oc/s$$
and $$\dfrac {R}{2}=-x(T' -30^oC)\ ^oc/s$$
from above
$$\Rightarrow \ -2k=-1\times k (T'-30^oC)\ \Rightarrow \ T'=10+30=40^oC$$ (required)
Question 4
1 / -0

When $$2 gm$$ of gas is introduced into an evacuated flask kept at $$25^oC$$ the pressure is found to be one atmosphere. If $$3 gm$$ of another gas added to the same flask the pressure becomes $$1.5$$ atmospheres. The ratio of the molecular weights of there gases will be

A
$$1:3$$

B
$$3:1$$

C
$$1:2$$

D
$$3:2$$

Solution
Question 5
1 / -0

In a waterfall the water falls from a height of 100 m. If the entire energy of water is converted into heat. The rise in temperature of water will be:

A
$$0.3^{o} C$$

B
$$0.46^{o} C$$

C
$$2.3^{o} C$$

D
$$0.23^{o} C$$

Solution
Question 6
1 / -0

A real gas most closely approaches the behaviour of an ideal gas at :

A
15 atm and 200 K

B
1 atm and 273 K

C
0.5 atm and 500 K

D
15 atm and 500 K

Solution
Question 7
1 / -0

Glaciers melt:

A
first at the bootom due to decress in pressure

B
first at the top due to iuncrease in pressure

C
first at the bottom due to increase in pressure

D
first at the top due to increase in pressure

Solution
Question 8
1 / -0

Two metal sphere have radii $$r$$ and $$2r$$ and they emit thermal radiation with maximum intensities at wavelength $$\lambda$$ and $$2 \lambda$$. The respective ratio of the radiant energy emitted by them per second will be

A
$$4:1$$

B
$$1:4$$

C
$$16:1$$

D
$$8:1$$

Solution
Question 9
1 / -0

The heat transferred by the radiator of a refrigerator is

A
more than that at the freezer

B
less than that at the freezer

C
the same as that at the freezer

D
none of these

Solution
Question 10
1 / -0

If the ratio of the coefficient of thermal conductivity of silver and copper is $$10: 9$$, then the ratio of the lengths up to which was will melt in Ingen Hauz experiment will be

A
$$6: 10$$

B
$$\sqrt{10}:3$$

C
$$100: 81$$

D
$$81: 100$$

Solution

Since $$K \propto l^2$$, $$K_1:K_1=l_1^2:l_2^2 \implies \dfrac{l_1}{l_2}=\sqrt{\dfrac{K_1}{K_2}}=\sqrt{\dfrac{10}{9}}=\dfrac{\sqrt{10}}{3}$$