Physics-DPP-1-14.Rotational Motion

PHYSICS Topic: ROTATIONAL MOTION Date: 1. The angular momentum of a projectile projected at angle θ with, the horizontal with speed u about the point of projection when it is at the highest point is : (a) mu2 sin2 θ g (b) mu cosθ g (c) mu3 sin2 θ cosθ (d) none of these 2g 2. Radius of gyration of a body about an axis at a distance of 4 cm from its centre of mass is 8 cm. The radius of gyration about a parallel axis through its centre of mass is : (a) 7 cm (b) 3 cm (c) 4 cm (d) none of these 3. The distance between the sun and earth be r then the angular momentum of the earth around the sun is proportional to : (a) (b) r3/ 2 (c) r (d) none of these 4. Initial angular velocity of a circular disc of mass M is ω1 . Then two small spheres of mass m are attached gently to two diametrically opposite points on the edge of the disc. What is the final angular velocity of the disc ? (a) æçM + çè m ö÷ ÷ 1 (b) æçM + ç m ö÷ ÷ 1 (c) æç M ö÷ (d) ç M ö÷ M ø è m ø èM + 4mø èM + 2mø 5. If a body completes a vertical circle, then : (a) total energy of body remains constant (b) angular momentum remains constant (c) angular velocity remains constant (d) none of the above 6. A circular disc X of radius R is made from an iron plate of thickness t, and another disc Y of radius 4 R is made from an iron plate of thickness t / 4. Then the relation between the moment of inertia IX and IY is : (a) IY = 32 IX (b) IY = 16 IX (c) IY = IX (d) IY = 64 IX 7. A particle performing uniform circular motion has angular momentum L. If its angular frequency is doubled and its kinetic energy halved, then the new angular momentum is : (a) L L 4 (b) 2 L (c) 4 L (d) 2 8. The moment of inertia of uniform semicircular disc of mass M and radius r about a line perpendicular to the plane of the disc through the centre is : (a) 1 Mr 2 4 (b) 2 Mr 2 5 (c) Mr2 (d) 1 Mr 2 2 9. The instantaneous velocity of point B of the given rod of length 0.5 m is 3 m/s in the represented direction. The angular velocity of the rod for minimum velocity of end A is : (a) 1.5 rad/s (b) 5.2 rad/s (c) 2.5 rad /s (d) none of these 10. A nearly massless rod is pivoted at one end so that it can swing freely as a pendulum. Two masses, 2 m and m, are attached to it at distance b and 3b, respectively, from the pivot. The rod is held horizontal and then released. Find its angular acceleration at the instant it released. (a) 2g / 11b (b) 4g/ 17 b (c) 5g / 11b (d) 5g / 12 b PHYSICS Topic: ROTATIONAL MOTION Date: Answer Key 1. (c) 2. (a) 3. (a) 4. (c) 5. (d) 6. (d) 7. (a) 8. (d) 9. (b) 10. (c)

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