Home
Class 12
PHYSICS
A disc is rotating with angular speed CD...

A disc is rotating with angular speed CD. If a child sits on it, what is conserved

A

linear momentum

B

angular momentum

C

kinetic energy

D

potential energy

Text Solution

Verified by Experts

The correct Answer is:
B
When a child sits on a rotating disc, no external torque is introduced. Hence the angular momentum of the system is conserved. But the moment of inertia of the system will increase and as a result, the angular speed of the disc will decrease to maintain constant angular momentum.
[`because` angular momentum = moment of inertia `xx` angular velocity]
Promotional Banner

Topper's Solved these Questions

  • MOTION OF CENTRE OF MASS, CONNECTED SYSTEMS, FRICTION

    MTG-WBJEE|Exercise WB-JEE Previous years questions|17 Videos

  • MOTION OF CENTRE OF MASS, CONNECTED SYSTEMS, FRICTION

    MTG-WBJEE|Exercise WB-JEE Previous years questions|17 Videos

  • MODEL TEST PAPTER

    MTG-WBJEE|Exercise MCQs|80 Videos

  • NUCLEAR PHYSIC

    MTG-WBJEE|Exercise WB JEE PREVIOUS YEARS QUESTIONS|5 Videos

Similar Questions

Explore conceptually related problems

A disc is rotating with angular velocity omega . If a child sits on it, what is conserved?

In previous problem, if initially the platform with the child is rotating with an angular speed omega_(1) . If child start walking along its periphery in opposite direction with speed u relative to platform, what will be the new angular speed ofthe platform.

A disc is rotating with angular speed omega_(1) . The combined moment of inertia of the disc and its axle is I_(1) . A second disc of moment of inertia I_(2) is dropped on to the first and ends up rotating with it. Find the angular velocity of the combination if the original angular velocity of the upper disc was (a) zero (b) omega_(2) in the same direction as omega_(1) and (c) omega_(2) in a direction opposite to omega_(1) .

A disc with moment of inertial I is rotating with some angular speed. Second disc is initially at rest. Now second disc with moment of inertia 3I is placed on first disc and starts rotating. Find loss of kinetic energy in fraction

A disc is freely rotating with an angular speed omega on a smooth horizontal plane. If it is hooked at a rigid pace P and rotates without bouncing about a point on its circumference. Its angular speed after the impact will be equal to.

A solid disc is rotating at an angular speed of 20 rad/s. It is decelerated at a constant rate of "2 rad/s"^(2) . Through what angle the disc will turn before coming to rest?

In the previous problem, initially the insect is at the edge and the disc is rotating with angular speed omega_(0) in clockwise direction. Now the insect starts walking along the rim with speed v relative to the disc also in clockwise direction. Find new angular speed of platfrom.

A child stands at the centre of a turn table with his two arms outstretched. The turn table is set rotating with an angular speed of 40 rpm. How much is the angular speed of the child, if he folds his hands back reducing the moment of inertia to (2//5) time the initial value ? Assume that the turn table rotates without friction. (b) Show that the child's new K.E. of rotation is more than the initial K.E. of rotation. How do you account for this increase in K.E. ?

(i) A child stands at the centre of turntable with his two arms out stretched. The turntable is set rotating with an angular speed of 40 rpm. How much is the angular speed of the child if he folds his hands back and thereby reduces his moment of inertia to (2)/(3) times the initial value ? Assume that the turntable rotates without friction (ii) Show that the child's new kinetic energy of rotation is more than the initial kinetic energy of rotation. How do you account for this increase in kinetic energy ?

MTG-WBJEE-MOTION OF CENTRE OF MASS, CONNECTED SYSTEMS, FRICTION-WB-JEE WORKOUT (CATEGORY 2 : Single Option Correct Type (2 Marks))
  1. A thin and circular disc of mass m and radius R is rotating in a horiz...

    Text Solution

    |

  2. A circular disc is to be made by using iron and aluminium so that it a...

    Text Solution

    |

  3. A disc is rotating with angular speed CD. If a child sits on it, what ...

    Text Solution

    |

  4. A solid cylinder of mass M and radius R rolls without slipping down an...

    Text Solution

    |

  5. From a circular disc of radius R and mass 9M, a small disc of radius R...

    Text Solution

    |

  6. A solid sphere of mass M, radius R and having moment of inertia about ...

    Text Solution

    |

  7. A cord is wound round the circumference of a wheel of radius r. The ax...

    Text Solution

    |

  8. A tube of length L is filled completely with an incompressible liquid ...

    Text Solution

    |

  9. A body takes twice the time to slides down a rough inclined plane at 4...

    Text Solution

    |

  10. Two discs of moments of inertia l(1) and l(2) and angular speeds omega...

    Text Solution

    |

  11. A thin wire of length L and uniform linear mass density p is bent into...

    Text Solution

    |

  12. A particle of mass m = 5 units is moving with a uniform speed v = 3sqr...

    Text Solution

    |

  13. Four spheres each having mass m and radius r are placed with their cen...

    Text Solution

    |

  14. A circular disc rolls down on an inclined plane without slipping. What...

    Text Solution

    |

  15. The moment of inertia of a thin square plate ABCD, as shown A in the f...

    Text Solution

    |

  16. A particle of mass m is projected with a velocity v making an angle of...

    Text Solution

    |

  17. A man stands at the centre of a circular table with his two hands outs...

    Text Solution

    |

  18. A small sphere S of radius ,r and mass m rolls without slipping, insid...

    Text Solution

    |

  19. The torque vectau on a body about a given point is found to be equal t...

    Text Solution

    |

  20. A small block of mass of 0.1 kg lies on a fixed inclined plane PQ whic...

    Text Solution

    |