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. A sample of 0.1 g of water at 100°C and normal pressure (1.013 x 10^{5} Nm^{-2}) requires 54 cal of heat energy to convert to steam at 100°C. If the volume of the steam produced is 167.1 cc, the change in internal energy of the sample, is
42.2 J
208.7 J
104.3 J
84.5 J
As we have learned
First law of Thermodynamics -
Heat imported to a body in is in general used to increase internal energy and work done against external pressure.
- wherein
Option 1)
42.2 J
This is incorrect
Option 2)
208.7 J
This is correct
Option 3)
104.3 J
This is incorrect
Option 4)
84.5 J
This is incorrect
Two wires are made of the same material and have the same volume, The first wire has cross-sectional area A and the second wire has cross-sectional area 3A. If the length of the first wire is increased by on applying a force F, how much force is needed to stretch the second wire by the same amount ?
4 F
6 F
9 F
F
The power radiated by a black body is P and it radiates maximum energy at wavelength, . If the temperature of the black body is now changed so that it radiates maximum energy at wavelength , the power
becomes nP. The value of n
A small sphere of radius `r' falls from rest in a viscous liquid. As a result, heat is produced due to viscous force. The rate of production of heat when the sphere attains its terminal velocity, is proportional to
r^{5}
r^{2}
r^{3}
r^{4}
A solid sphere is in rolling motion. In rolling motion a body possesses translational kinetic energy (K_{t}) as well as rotational kinetic energy
(K_{r}) simultaneously. The ratio K_{t} : (K_{t }+ K_{r}) for the sphere is
10 : 7
5 : 7
7 : 10
2 : 5
If the mass of the Sun were ten times smaller and the universal gravitational constant were ten times larger in magnitude, which of the following is not correct ?
Time period of a simple pendulum on the Earth would decrease.
Walking on the ground would become more difficult.
Raindrops will fall faster.
'g' on the Earth will not change.
The kinetic energies of a planet in an elliptical orbit about the Sun, at positions A, B and C are K_{A}, K_{B} and K_{C}, respectively. AC is the major axis and SB is perpendicular to AC at the position of the Sun S as shown in the figure. Then
A solid sphere is rotating freely about its symmetry axis in free space. The radius of the sphere is increased keeping its mass same. Which of the following physical quantities would remain constant for the sphere ?
Rotational kinetic energy
Moment of inertia
Angular velocity
Angular momentum
The moment of the force , at (2, 0 , -3 ) ,about the point (2, -2 , -2 ) is given by
A block of mass m is placed on a smooth inclined wedge ABC of inclination as shown in the figure. The wedge is given an acceleration 'a' towards the right. The relation between a and for the block to remain stationary on the wedge is
4) a =gtan
A toy car with charge q moves on a frictionless horizontal plane surface under the influence of a uniform electric field . Due to the force q , its velocity increases from 0 to 6 m/s in one second duration. At that instant the direction of the field is reversed. The car continues to move for two more seconds under the influence of this field. The average velocity and the average speed of the toy car between 0 to 3 seconds are
respectively
1 m/s, 3.5 m/s
1 m/s , 3 m/s
2 m/s , 4 m/s
1.5 m/s , 3 m/s
Which one of the following statements is incorrect ?
Frictional force opposes the relative motion.
Limiting value of static friction is directly proportional to normal reaction.
Rolling friction is smaller than sliding friction.
Coefficient of sliding friction has
dimensions of length.
A moving block having mass m, collides with another stationary block having mass 4m. The lighter block comes to rest after collision. When the initial velocity of the lighter block is v, then the value of coefficient of restitution (e) will be
0.8
0.25
0.5
0.4
Three objects, A : (a solid sphere), B : (a thin circular disk) and C : (a circular ring), each have the same mass M and radius R. They all spin with the same angular speed about their own symmetry axes. The amounts of work (W) required to bring them to rest, would satisfy the relation
A body initially at rest and sliding along a frictionless track from a height h (as shown in the figure) just completes a vertical circle of diameter AB = D. The height h is equal to
An inductor 20 mH, a capacitor 100 F and a resistor 50 are connected in series across a source of emf V = 10 sin 314 t. The power loss in circuit is
2.74 W
0.43 W
0.79 W
1.13 W
A thin diamagnetic rod is placed vertically between the poles of an electromagnet. When the current in the electromagnet is switched on, then the diamagnetic rod is pushed up, out of the horizontal magnetic field. Hence the rod gains gravitational potential energy. The work required to do this comes from
the lattice structure of the material of the rod
the magnetic field
the current source
the induced electric field due to the changing magnetic field
A metallic rod of mass per unit length 0.5 kg m^{-1 }is lying horizontally on a smooth inclined plane which makes an angle of 30^{o} with the horizontal. The rod is not allowed to slide down by flowing a current through it when a magnetic field of induction 0.25 T is acting on it in the vertical direction. The current flowing in the rod to keep it stationary is
14.76 A
5.98 A
7.14 A
11.32 A
The electrostatic force between the metal plates of an isolated parallel plate capacitor C having a charge Q and area A, is
proportional to the square root of the distance between the plates.
linearly proportional to the distance between the plates.
independent of the distance between the plates.
inversely proportional to the distance between the plates.