Rotational Motion

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Topics

• Centre of mass of two-particle system and rigid body 3
• Moment of force, torque 3
• Angular momentum and its conservation 3
• Moment of inertia, radius of gyration, MI of simple objects 9
• Equilibrium of rigid bodies, rigid body rotation, equations of rotational motion 6
• Comparison of linear and rotational motion 4

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• Physics: Rotational Motion – NEET practice test Practice set · NEET · 27 questions · 27 min

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• The Sun rotates around its centre once in 27 days. What will be the period of revolution if the Sun were to expand to twice its present radius without any external influence? Assume the Sun to be a sphere of uniform density. Answer: 4. 108 days Key idea: no external torque, so angular momentum L=Iω is conserved. For a uniform sphere, I=2/5MR² . Mass stays the sam... Angular momentum and its conservation 1 answer
• A uniform rod of mass 20 kg and length 5 m leans against a smooth vertical wall making an angle of 60^° with it. The other end rests on a rough horizontal floor. The friction force that the floor exerts on the rod is (take g = 10 m/s^2) Answer: 2. 100√(3) N Key idea: the wall is smooth, so the wall force N is horizontal. For equilibrium, floor friction f equals N , and torqu... Equilibrium of rigid bodies, rigid body rotation, equations of rotational motion 1 answer
• A sphere of radius R is cut from a larger solid sphere of radius 2R as shown in the figure. The ratio of the moment of inertia of the smaller sphere to that of the rest part of the sphere about the Y-axis is : Answer: 3. 7/57 Key idea: moment of inertia of the remaining part = full sphere - removed sphere, using the parallel-axis theorem for the cu... Moment of inertia, radius of gyration, MI of simple objects 1 answer
• A wheel of a bullock cart is rolling on a level road as shown in the figure below. If its linear speed is v in the direction shown, which one of the following options is correct (P and Q are any highest and lowest points on the wheel, respectively)? Answer: 3. Point P moves faster than point Q . Key idea: In pure rolling, each point has speed = (speed of centre) + (rotational speed about... Equilibrium of rigid bodies, rigid body rotation, equations of rotational motion 1 answer
• The moment of inertia of a thin rod about an axis passing through its mid point and perpendicular to the rod is 2400 g cm^2. The length of the 400 g rod is nearly : Answer: 2. 8.5 cm Key idea: For a thin rod about its midpoint and perpendicular to its length, I=ML²/12 . L²=12I/M=12×2400/400=72 , so L=√(7... Moment of inertia, radius of gyration, MI of simple objects 1 answer
• The ratio of radius of gyration of a solid sphere of mass M and radius R about its own axis to the radius of gyration of the thin hollow sphere of same mass and radius about its axis is : Answer: Dropped in the official answer key: full marks to every candidate Radius of gyration is k=√(I/M) . Solid sphere about its axis: I=2/... Moment of inertia, radius of gyration, MI of simple objects 1 answer