Category: Class 11 Physics Objective Questions

Physics Multiple Choice Questions on “Universal Law of Gravitation”.

1. For which of the following does the graph denote the variation of force of gravity “F” along a distance “r”?

a) Solid sphere
b) Spherical shell
c) Plate
d) Point
Answer: b
Clarification: The force of gravity is zero withing a spherical shell and varies similar to a point source at a distance greater than or equal to its radius.

2. For which of the following does the graph denote the variation of force of gravity “F” along a distance “r”?

a) Solid sphere
b) Spherical shell
c) Plate
d) Point
Answer: a
Clarification: The gravitational force is proportional to distance “r” until r=radius. For values of “r” greater than the radius of the sphere, the force is inversely proportional to the square of the distance.

3. What is the gravitational force experienced by an object of 10kg 200m away from an object weighing 1 ton?
a) 1.6675 N
b) 2.6675 N
c) 3.6675 N
d) 4.6675 N
Answer: a
Clarification: From Newton’s law of gravitation, we have;
F = (G*M1*M2*)/R²
G = 6.67 x 10^-11 N m²/kg²
M1 = 10kg
M2 = 1000kg
R = 200m
F = (6.67 x 10^-11 x 10 x 1000) / 200²
= 1.6675 N.

4. Which scientist introduced the universal law of gravitation?
a) Albert Einstein
b) Isaac Newton
c) Stephen Hawking
d) Nikola Tesla
Answer: b
Clarification: The universal law of gravitation is a part of Isaac Newton’s work “Philosophiæ Naturalis Principia Mathematica (the Principia)”, first published on 5 July 1687.

5. What will be the value of acceleration due to gravity on the surface of the earth if the radius of the earth suddenly decreases to 60% of its present value, keeping the mass of the earth unchanged?
a) 9.81 m/s²
b) 5.89 m/s²
c) 16.35 m/s²
d) 27.25 m/s²
Answer: d
Clarification: From Newton’s law of gravitation, we have;
g = (G*M1)/R²
Since the radius is reduced to 60% of its original value;
The new radius R’ = 0.6 x R
Therefore;
g’ = (G*M1)/(0.6*R) ²
g’ = g/(0.6) ²
= 9.81 / (0.6 x 0.6)
g’ = 27.25 m/s².

6. The value of acceleration due to gravity of earth at the equator is less than that of the poles due to _____
a) shape and rotation of the earth
b) mass of the sun
c) mass of the earth
d) mass of the moon
Answer: a
Clarification: The gravitational force is a central force. Acceleration due to gravity has different values for different points on the earth’s surface.

7. The weight of an object can be zero but the mass of an object can never be zero.
a) True
b) False
Answer: a
Clarification: The weight of an object is zero when the net gravitational force acting on the object is zero. However, the mass of an object can never be zero since mass is a property of matter.

8. Gravitational force is the strongest fundamental force.
a) True
b) False
Answer: b
Clarification: Gravitational force is the weakest fundamental force. The strong nuclear force is the strongest fundamental force of nature.

9. Gravitational force is _____
a) an imaginary force
b) a long-range force
c) a short-range force
d) the strongest fundamental force
Answer: b
Clarification: Gravitational force is a long-range force which is inversely proportional to the square of the distance. The strong nuclear force is the strongest fundamental force and is a short-range force.

10. The universal law of gravitation becomes more inapplicable as the size and distance between objects decreases.
a) True
b) False
Answer: a
Clarification: As the size and distance between objects decrease, nuclear forces become stronger and the law of gravitation cannot be applied. This calls for a new branch of physics known as “quantum physics”.

11. What is the force of gravity experienced by an object at the centre of the earth? (Assume that the earth is perfectly spherical)
a) 0 g-force
b) 1 g-force
c) 9.81 g-force
d) 10 g-force
Answer: a
Clarification: Since a body at the centre of the earth would experience equal gravitational force from all sides, the vector addition of all of these forces amount to zero. Therefore, the force experienced by an object at the centre of the earth is zero.

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Physics Online Test for Class 11 on “Thermodynamics – Heat, Internal Energy and Work”.

1. Internal energy of a system is defined as?
a) The sum of kinetic energies of all molecules of the system
b) The sum of kinetic and potential energies of all molecules of the system
c) The sum of potential energies of the system
d) The average kinetic energy of all molecules
Answer: b
Clarification: The internal energy of a system corresponds to the energy possessed by all molecules. Thus it is the sum of kinetic and potential energies of all molecules in the system considered. Also note that potential energy is frame dependent, so we choose a frame in which the centre of mass is at rest.

2. Select the correct statement.
a) Internal energy is a path variable
b) Heat is a path variable
c) Work done is a state variable
d) Internal energy is a microscopic variable
Answer: b
Clarification: Internal energy corresponds to the mechanical energy of molecules. It is a state variable as it doesn’t depend on the path taken. While heat is the energy in transit, so it is a path variable. Internal energy is a thermodynamic variable and is therefore macroscopic as thermodynamics deals with bulk systems.

3. A box contains 10⁵ molecules. The average kinetic energy of each molecule is 0.5*10^-6J. With respect to an observer at rest the box, having a mass of 1kg, is moving with a velocity of 2m/s. What is the value of kinetic energy that will contribute to the internal energy?
a) 0.05J
b) 2.05J
c) 0
d) 2J
Answer: a
Clarification: When calculating internal energy of molecules, the system is to be studied from a frame in which the centre of mass is at rest. So the kinetic energy due to movement of the entire box will not be considered. Only the individual kinetic energies of molecules will be considered, and their value is: 10⁵*0.5*10^-6
= 0.05J.

4. If some heat is provided to a system and work is done on it, it is possible that internal energy will decrease. True or False?
a) True
b) False
Answer: b
Clarification: Internal energy corresponds to the mechanical energy of the molecules. When these molecules are provided with heat and are compressed their mechanical energy will increase. Both factors support the increase of internal energy hence the given statement is false.

5. Which of the following types of kinetic energies contribute to internal energy?
a) Translational
b) Rotational
c) Vibrational
d) Translational, Vibrational & Rotational
Answer: d
Clarification: Internal energy consists of the total kinetic energy of all molecules, which means all types, namely translational, rotational & vibrational kinetic energies contribute to internal energy.

6. A body has 15J of heat energy in a particular state. At the same state it has an internal energy of 30J. Assume no work is done, what will happen to the internal energy if 5J of heat is added to the system?
a) Heat energy = 20J, Internal energy = 35J
b) Heat energy = 15J, Internal energy = 30J
c) Heat energy = 15J, Internal energy = 35J
d) A body cannot have heat energy in a particular state
Answer: d
Clarification: Heat energy is the energy in transit. A system’s state cannot be defined by heat energy, it is defined by internal energy. Heat and work are path functions. Heat can be supplied or removed from a system but can’t define a system in a state.

To practice Physics Online Test for Class 11,

Physics Quiz Online for Class 11 on “Oscillations – Velocity and Acceleration in Simple Harmonic Motion”.

1. A particle is executing SHM and currently going towards the amplitude. If it is at A/2, what is the relation between the direction of velocity and acceleration?
a) Both vectors point towards the amplitude
b) Velocity is towards amplitude & acceleration is towards mean position
c) Velocity is towards mean position & acceleration is towards the amplitude
d) Both vectors point towards the mean position
Answer: b
Clarification: The force on a particle in SHM is always towards the mean position. The particle is currently going towards an extreme, thus velocity will be towards the amplitude.

2. In a SHM, for what value of w, will the magnitude of maximum acceleration be greater than the magnitude of maximum velocity? Here, w is angular frequency.
a) w > 1
b) w < 1
c) w = 0
d) Not possible for any value of w
Answer: a
Clarification: Let the velocity equation of SHM be: v = Awcos(wt),
acceleration will be given by: a = -Aw²sin(wt).
Maximum magnitude of vel = Aw
Maximum magnitude of acc = Aw².
For, Aw² > Aw
w > 1.

3. A particle of mass m starts from the mean position of a SHM, at t=0, and goes towards -A. If the angular frequency of SHM is w, find the force acting on it as a function of time.
a) mAw²sin(wt)
b) mAw²sin(wt+π)
c) -mAw²cos(wt+π)
d) -mAw²cos(wt)
Answer: a
Clarification: The displacement equation will be given by: x = -Asin(wt).
On taking its derivative, we get:
v = -Awcos(wt).
Further, we get: a = Aw²sin(wt).
Thus, force is given by: F(t) = mAw²sin(wt).

4. The graph of acceleration vs time for a SHM is given. FInd the equation of position of the particle as a function of time. Assume that the particle is oscillating on the x-axis about the origin. And consider RHS of origin to be positive & LHS to be negative.

a) 8cos(πt)
b) -8cos(πt)
c) 0.81sin(πt)
d) -0.81sin(πt)
Answer: d
Clarification: The particle has zero acceleration at t=0, so it starts from the mean position. Then the acceleration becomes positive which implies that the particle is moving towards -A ( negative extreme). The equation of acceleration can be given by: a = 8sinwt.
The time period is 2s,
so w = 2π/2 = πs^-1.
∴ a = 8sin(πt).
∴ v = -8/π cos(πt)
∴ x = -8/pi²sin(πt) = -0.81sin(πt).

5. A particle is undergoing a SHM of amplitude 10cm. What should be the minimum value of acceleration at an extreme position for maximum speed at centre to be 5m/s?
a) 20m/s²
b) 5m/s²
c) 0
d) 250m/s²
Answer: d
Clarification: v_max = Aw.
5 = 0.1w.
w = 50s^-1.
a_min at extreme = Aw²
= 0.1*50*50
= 250m/s².

6. A particle in uniform circular motion is projected on its diameter. The motion of projection will be simple harmonic. Select the correct option regarding speed and acceleration of the particle in circular motion.
a) Speed is constant, acceleration is zero
b) Speed is constant, acceleration is non-zero
c) Speed changes, acceleration is non-zero
d) Speed changes, acceleration is zero
Answer: a
Clarification: For the particle in uniform circular motion, magnitude of velocity is constant, but direction is continuously changing. Thus, speed is constant but acceleration is non-zero.

7. The curves given below are that of position(x), velocity(v) & acceleration(a) vs time. What can we infer about the value of angular frequency ‘f’ from the given curves?

a) f > 1
b) f < 1
c) f = 0
d) We need the time period in order to find ‘f’
Answer: a
Clarification: Amplitude of position = A
Amplitude of velocity = Af
Amplitude of acceleration = Af².
From the graph we deduce that the amplitude of a is greater than the amplitude of v which in turn is greater than the amplitude of x.
Thus, angular frequency will be greater than 1.

To practice Physics Quiz Online for Class 11,

Physics Multiple Choice Questions on “Introduction to Motion in a Straight Line”.

1. In which of the following states does a body possess kinetic energy?
a) Rest
b) Motion
c) When placed on a platform
d) In zero gravity
Answer: b
Clarification: The body moves in the state of motion. Hence it has a velocity and so kinetic energy. Kinetic energy = (1/2)mv².

2. Which of the following types of motion can be used for describing the motion of a car on a straight road?
a) Rectilinear
b) Circular
c) Periodic
d) Harmonic
Answer: a
Clarification: The motion of a car on straight road is happening along a straight line. Hence the motion can be called rectilinear as rectilinear motion happens along a straight line. Rest all are non rectilinear motions.

3. Which of the following types of motion cannot describe the motion of a clock’s hands?
a) Rectilinear
b) Circular
c) Periodic
d) Harmonic
Answer: a
Clarification: The hands of a clock move in a circular manner. Hence, the motion exhibited is circular motion. Moreover, it happens periodically, so it is also periodic motion. But its is not rectilinear motion.

4. Which force can possibly act on a body moving in a straight line?
a) Tangential force
b) Friction force
c) Centrifugal force
d) Centripetal force
Answer: b
Clarification: In the physical world, no surface is frictionless. Hence whenever a body moves, the force of friction acts on it. Rest all forces act on the body only when it moves along a curve and not along a straight line.

5. What kind of motion is rectilinear motion?
a) One dimensional
b) Two dimensional
c) Three dimensional
d) Zero dimensional
Answer: a
Clarification: Rectilinear motion happens along a straight line. A straight line is one dimensional. Hence, rectilinear motion is one dimensional.

6. When a body is in the state of complete rest, what kind of energy does it possess?
a) Potential energy
b) Kinetic energy
c) Total energy
d) Heat energy
Answer: a
Clarification: When the body is in the state of rest, there is no motion. Hence there is no kinetic energy, hence the total energy of the body is stored as its potential energy. The total energy is the sum of kinetic and potential energies.

7. Which of the following are obtained by dividing total displacement by total time taken?
a) Average velocity
b) Instantaneous velocity
c) Uniform velocity
d) Speed
Answer: a
Clarification: The average velocity is obtained by dividing total displacement by total time taken. Instantaneous velocity is calculated at an instant and not over a period of time. Speed is distance divided by time. Velocity is said to be uniform when velocity at every instant is equal to the average velocity.

8. What is the rate of change of rate of change of displacement of a body?
a) Velocity
b) Acceleration
c) Force
d) Jerk
Answer: b
Clarification: The rate of change of displacement of a body is velocity. The rate of change of rate of displacement of a body, or rate of change of velocity is acceleration.

Physics,