NCERT Solutions For Class 11 Physics Chapter 7: System of Particles and Rotational Motion

NCERT Solutions for Class 11 Physics Chapter 7 System of Particles and Rotational Motion covers all the concepts discussed in the Class 11 Physics Chapter 7. The combination of rotational motion and the translational motion of a rigid body is known as rolling motion. According to the law of conservation of angular momentum, if there is no external couple acting, the total angular momentum of a rigid body or a system of particles is conserved.

Class 11 Physics Chapter 7 System of Particles and Rotational Motion has a weightage of 17 marks along with Unit 4 Work, Energy, and Power and Unit 6 Gravitation. The Class 11 Physics Chapter 7 discusses the concepts of TorqueAngular Momentum, and Rotational Kinetic Energy.

Download PDF: NCERT Solutions for Class 11 Physics Chapter 7


NCERT Solutions for Class 11 Physics Chapter 7

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Class 11 Physics Chapter 7 – Concepts Covered

  • Centre of MassFor a system of particles, the centre of mass is the balancing point where the entire mass of the system is concentrated, for consideration of its translational motion.

If there are 2 particles with mass m1 and m2 with position vectors \(\overrightarrow{r_1}\ and\ \overrightarrow{r_2}\), then the position vector of centre of mass is given as:

\(\overrightarrow{r_{cm}} = {{m_1}\overrightarrow{r_{1}} + {m_2}\overrightarrow{r_{2}} \over m_1 + m_2}\)

  • The cross product of two vectors \(\overrightarrow{A}\) and \(\overrightarrow{B}\) is another vector \(\overrightarrow{C}\), which has a magnitude equal to the product of the magnitudes of 2 vectors and the sine of the smaller angle \(\theta\) between them.
\(\overrightarrow{A} \times \overrightarrow{B} = \overrightarrow{C} = ABsin\theta \hat{c}\)
  • Torque or moment of force is the product of the magnitude of the force acting on a particle and the perpendicular distance of the application of this force from the axis of rotation of the particle.
\(Torque = Force \times perpendicular\ distance\)
  • The angular momentum about an axis of rotation is a vector quantity, with a magnitude equal to the product of the magnitude of momentum and the perpendicular distance of the line of action of momentum from the axis of rotation. Its direction is perpendicular to the plane that contains the momentum and the perpendicular distance.

\(\overrightarrow{L} = \overrightarrow{r} \times \overrightarrow{p} \)

  • Torque and angular momentum are correlated to each other.
\(\tau = {\overrightarrow{dL} \over dt}\)

CBSE CLASS XII Related Questions

1.
A capillary tube of radius r is dipped inside a large vessel of water. The mass of water raised above water level is M. If the radius of capillary is doubled, the mass of water inside capillary will be

    • 5M
    • 2M
    • \(\frac M4\)

    • M

    2.
    Two charges 5 × 10–8 C and –3 × 10–8 C are located 16 cm apart. At what point(s) on the line joining the to charges is the electric potential zero? Take the potential at infinity to be zero.

        3.

        Three capacitors each of capacitance 9 pF are connected in series. 

        (a) What is the total capacitance of the combination? 

        (b) What is the potential difference across each capacitor if the combination is connected to a 120 V supply?

            4.
            A boy of mass 50 kg is standing at one end of a, boat of length 9 m and mass 400 kg. He runs to the other, end. The distance through which the centre of mass of the boat boy system moves is

              • 0
              • 1 m

              • 2 m

              • 3 m

              5.
              A spherical conductor of radius 12 cm has a charge of 1.6 × 10–7C distributed uniformly on its surface. What is the electric field ?
              1. inside the sphere
              2. just outside the sphere
              3. at a point 18 cm from the centre of the sphere?

                  6.
                  A closely wound solenoid of \(2000 \) turns and area of cross-section \(1.6 × 10^{-4}\  m^2\), carrying a current of \(4.0 \ A\), is suspended through its centre allowing it to turn in a horizontal plane. 
                  (a) What is the magnetic moment associated with the solenoid?
                  (b) What is the force and torque on the solenoid if a uniform horizontal magnetic field of \(7.5 × 10^{-2}\  T\) is set up at an angle of \(30º\) with the axis of the solenoid?

                      CBSE CLASS XII Previous Year Papers

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