NCERT Solutions For Class 11 Physics Chapter 5: Laws of Motion

NCERT Solutions for Class 11 Physics Chapter 5 Laws of Motion are provided in the article below. The branch of physics where we study the motion of a body by considering the cause which is the force which generates the motion is called Dynamics. Newton’s three laws of motion make us understand how objects act when standing still, while moving or when forces behave upon them. 

Class 11 Physics Chapter 5 Laws of Motion belongs to Unit 3 which has a weightage of 23 marks along with Unit 2 Kinematics and Unit 3. The Class 11 Physics Chapter 5 NCERT Solutions deals with the concepts of force and Laws of Motion, Non-contact force, Inertia and Mass.

Download PDF: NCERT Solutions for Class 11 Physics Chapter 5


NCERT Solutions for Class 11 Physics Chapter 5

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Class 11 Physics Chapter 5 – Concepts Covered

  • Newton’s First Law of Motion is referred to as the “Law of Inertia”. The law defines inertia, an inertial frame of reference, and force.
A body will remain at rest or continue to be in motion with a uniform velocity unless an external force is applied to it.
  • Newton’s Second Law of Motion: When an external force is applied to a body with constant mass, the force produces an acceleration. The acceleration that is produced is directly proportional to the force and then inversely proportional to the mass of the body.
\(\overrightarrow {F} = K {dP \over dt} = Km \overrightarrow a\)
When body A exerts a force on some other body B, then B exerts an equal and opposite force on A.
  • Linear momentum of a body is the product of the mass and velocity of the body.

Linear Momentum = mass x velocity 

  • Impulse is the product of force and the small-time interval for which the force acts. 
\(Impulse= \int Fdt\)

CBSE CLASS XII Related Questions

  • 1.
    Read the following paragraph and answer the questions that follow.
    In an experiment with convex lens of focal length f, the screen is fixed at a distance D from the object. A student slowly moves the lens away from the object towards the screen and finds that she is able to form sharp image of the object for two positions of the lens. The distance between these two positions of the lens is d.


      • 2.
        An astronomical telescope consists of two converging lenses. One of them of large aperture and large focal length is called objective lens and the other one, of smaller focal length and smaller aperture is called the eyepiece. It is used to see distant objects which are not seen clearly with naked eyes. The image formed by the objective lens acts as an object for the eyepiece and the final image produced by the eyepiece is magnified.


          • 3.
            Consider the nuclear reaction \( X \to Y + Z \). Let \( M_x \), \( M_y \), and \( M_z \) be the masses of the three nuclei X, Y, and Z respectively. Then which of the following relations hold true?

              • \( (M_x - M_z)<M_y \)
              • \( (M_x - M_y)<M_z \)
              • \( M_x>(M_y + M_z) \)
              • \( M_x<(M_y + M_z) \)

            • 4.
              An electric field $\vec{E}$ is established across the ends of a cylindrical conductor of length L and area of cross-section A. Discuss how electrons attain an average velocity, independent of time. Hence, obtain a relation between current in the conductor and this ‘average velocity’ of electrons.


                • 5.
                  Two metal spheres of radii $r_1$ and $r_2$ ($> r_1$) having charges $q_1$ and $q_2$ respectively kept in air, are brought in contact. Which of the following statements is not correct ?

                    • The total charge of the two spheres is conserved.
                    • Both spheres attain the same potential.
                    • The final potential of the system equals $\frac{1}{4\pi\epsilon_0} \frac{(q_1 + q_2)}{(r_1 + r_2)}$
                    • The final potential of the system equals $\frac{1}{4\pi\epsilon_0} \frac{(q_1 + q_2) (r_1 + r_2)}{r_1 r_2}$

                  • 6.
                    A charged particle $+q$ in an electric field $\vec{E}$ experiences a force in the direction of the electric field. As a result, its kinetic energy changes. Similarly, the charged particle also experiences a force when it moves in a magnetic field $\vec{B}$. But this magnetic force is perpendicular to both velocity $\vec{v}$ of the charged particle and the magnetic field $\vec{B}$, so it cannot change the kinetic energy of the charged particle. Consider two charged particles 1 and 2 of masses $m$ and $\frac{m}{2}$ having charges $-q$ and $+2q$ respectively. They are accelerated from rest through the same potential difference $V$ and acquire kinetic energy $K_1$ and $K_2$. Then they enter in a region of uniform magnetic field $\vec{B}$ perpendicular to their velocities.

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