Physics: Topic-wise Test- 2 - NEET MCQ

By theorem of parallel axes

Firstly, using the relations given in the questions, we will find the length and mass of the parts


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The two masses are at a distance of “a” and “a/2” so,

By the principle of superposition of fields

Here  = net field at the centre of hole due to entire mass

 = field due to remaining mass

 = field due to mass in hole = 0

Let the acceleration due to gravity at that height is g′.

The acceleration due to gravity at some height (g′ ) = 1% of the acceleration due to gravity(g ) at the surface of the earth.

According to question

g′ = 1% of g

g′ = 1 / 100 × g

g′ = g / 100

The acceleration due to gravity at a height h above the surface of the earth is;

g′ = g (R / R+h)² , Where R is the radius of the earth.

Thus,

g / 100 = g(R / R+h)²

1 / 100 = (R / R+h)²

Taking square root on both sides we get,

1 / 10 = (R / R+h)

R+h = 10R

h = 9R

W = increase in potential energy of system

=U_f - U_i

=m (V_f - V_i)

(V = gravitational potential)

Note: Even if mass is nonuniformly distributed potential at centre would be -GM/R

From conservation of mechanical energy

I took g = 10 but if g = 9.8 is taken then we get the exact answer.

We know that the efficiency of refrigeration for a refrigerator is T₂ / T₁ + T₂
Where T₁ is source temperature and T₂ is sink temperature
For refrigerator X we have T₁ = 298K and T₂ = 268K
Hence the efficiency of refrigeration = 268 / 298 - 268
= 268 / 30
= 8.93
For refrigerator Y we have T₁ = 293K and T₂ = 253K
Hence the efficiency of refrigeration = 253 / 293 - 253
= 253 / 40
= 6.35

It works on the principle that no machine is 100% efficient. For instance if taking an ideal machine into consideration, work can be completely converted to heat. Now if the conditions are reversed, all heat cannot be converted to equal amount of work until and unless backed up by an external force.

A heat pump is an electrical device that heats a building by pumping heat in from the cold outside. In other words, it’s the same as a refrigerator, but its purpose is to warm the hot reservoir rather than to cool the cold reservoir (even though it does both).

The second law of thermodynamics gives a fundamental limitation to the efficiency of a heat engine and the coefficient of performance of a refrigerator. It says that the efficiency of a heat engine can never be unity or 100%, this implies that the heat released to the cold reservoir can never be made zero.
For a refrigerator the second law says that the coefficient through performance can never be infinite, this implies that the external work can never be zero.

If you leave the door open, heat is merely recycled from the room into the refrigerator, then back into the room. A net room temperature increase would result from the heat of the motor that would be constantly running to move energy around in a circle.

Zeroth law states that if two thermodynamic systems are each in thermal equilibrium with a third one, then they are in thermal equilibrium with each other. Thus as it deals with thermal equilibrium it is very clear that it is a concept of temperature.

∆ U = ∆ Q - ∆ W
In an adiabatic process ∆Q is zero, therefore
∆ U = - ∆ W

No, heat is not transferred as the flask is insulated from the surroundings ∴dQ=0

The internal energy of a system decreases by the same amount as the work done by the system.
 
Change in internal energy=work done+heat exchange
change in internal energy=work done if process has no heat exchange, i.e. it's adiabatic and the temperature must decrease
 

Wall that permits *heat" to flow through them,such as engine block is called diathermic wall.
wall Perfectly insulating ball that doesn't allow the flow heat to them are called adiabatic walls.

The rate of heat transfer is directly proportional to the bisectional surface area of the solid and inversely proportional to its parallel length. 
That is heat conduction rate say H ∝ r²
∝ 1/L
I.e ∝ r²/L
Hence the conduction would be
maximum in case in which  r²/L ratio is largest.

The Celsius and Fahrenheit are two important temperature scales. The Fahrenheit scale is used primarily in the United States, while Celsius is used throughout the world. The two scales have different zero points and the Celsius degree is bigger than the Fahrenheit one. There is one point on the Fahrenheit and Celsius scales where the temperatures in degrees are equal. This is -40 degree C and -40 degree F.

When heated the length between adjacent markings increases. Hence the actual length will be less than
30 cm.

Gas expands more than solid and liquid because gas particles are far apart hence freely move.

Young's Modulus of elasticity =stress/strain
Y= [F/a/△l/l] ​ or Y= [Fl​/a△l]
or △l= [Fl/aY] ​= Fl​/ πr²Y
In the given problem, △l∝ l​/ r²
When both l and r are doubled, △l is halved.

Stress = Force per area and strain is unit less.
Therefore in CGS units dyne per cm square.
Hence A is correct.

We know that magnitude of bulk modulus
K=[P/(dV/V)]
Now, percentage change in volume is. 10^-3 %
Therefore, (dV/V)x100=10^-3
So, dV/V=10^-5
Hence, k is,
K=40atm/10^-5=40x1.01x10⁵ /10^-5 =4.04x10¹¹ N/m²