Maharashtra Board Class 12 Physics Solution Chapter 1 – Rotational Dynamics
Balbharati Maharashtra Board Class 12 Physics Solution Chapter 1: Rotational Dynamics. Marathi or English Medium Students of Class 12 get here Rotational Dynamics full Exercise Solution.
Std |
Maharashtra Class 12 |
Subject |
Physics |
Chapter |
1 |
Chapter Name |
Rotational Dynamics |
Q.1. Choose the correct option.
i.) When seen from below, the blades of a ceiling fan are seen to be revolving anticlockwise and their speed is decreasing. Select correct statement about the directions of its angular velocity and angular acceleration.
(A) Angular velocity upwards, angular acceleration downwards.
(B) Angular velocity downwards, angular acceleration upwards.
(C) Both, angular velocity and angular acceleration, upwards.
(D) Both, angular velocity and angular acceleration, downwards.
Answer:
(B) Angular velocity downwards, angular acceleration upwards.
According to right hand screw rule, thumb denotes the direction of angular velocity. If the velocity is increases then angular acceleration is also towards the direction of thumb, but if the velocity decreases the angular acceleration is opposite to direction of angular velocity.
ii.) A particle of mass 1 kg, tied to a 1.2 m long string is whirled to perform vertical circular motion, under gravity. Minimum speed of a particle is 5 m/s. Consider following statements.
P) Maximum speed must be 5 5 m/s.
Q) Difference between maximum and minimum tensions along the string is 60 N. Select correct option.
(A) Only the statement P is correct.
(B) Only the statement Q is correct.
(C) Both the statements are correct.
(D) Both the statements are incorrect.
Answer:
(B) Only the statement Q is correct.
iii.) Select correct statement about the formula (expression) of moment of inertia (M.I.) in terms of mass M of the object and some of its distance parameter/s, such as R, L, etc.
(A) Different objects must have different expressions for their M.I.
(B) When rotating about their central axis, a hollow right circular cone and a disc have the same expression for the M.I.
(C) Expression for the M.I. for a parallelepiped rotating about the transverse axis passing through its centre includes its depth.
(D) Expression for M.I. of a rod and that of a plane sheet is the same about a transverse axis.
Answer:
(B) When rotating about their central axis, a hollow right circular cone and a disc have the same expression for the M.I.
Moment of inertia of disc of mass M and radius R about central axis is,
M.I. of disc = 〖MR〗^2/2
Moment of inertia of hollow cylinder of mass M and radius R about central axis is,
M.I. of cylinder = 〖MR〗^2/2
iv.) In a certain unit, the radius of gyration of a uniform disc about its central and transverse axis is . Its radius of gyration about a tangent in its plane (in the same unit) must be
(A √2.5
(B) 2.5
(C) 2√2.5
(D) √12.5
Answer:
(B) 2.5
v.) Consider following cases:
(P) A planet revolving in an elliptical orbit.
(Q) A planet revolving in a circular orbit.
Principle of conservation of angular momentum comes in force in which of these?
(A) Only for (P)
(B) Only for (Q)
(C) For both, (P) and (Q)
(D) Neither for (P), nor for (Q)
Answer:
(C) For both, (P) and (Q)
Law of conservation of angular momentum holds good for every rotational motion irrespective of the path of rotation.
vi.) A thin walled hollow cylinder is rolling down an incline, without slipping. At any instant, the ratio ”Rotational K.E.: Translational K.E.: Total K.E.” is
(A) 1:1:2
(B) 1:2:3
(C) 1:1:1
(D) 2:1:3
Answer:
(D) 2:1:3
Here,