Physics-DPP-3-3.CENTRE OF MASS, CONSERVATION OF MOMENTUM, COLLISION

PHYSICS Topic: CENTRE OF MASS, CONSERVATION OF MOMENTUM, COLLISION Date: 1. Two vehicles of equal masses are moving with same speed v on two roads inclined at an angle θ . They collide inelastically at the junction and, then move together. The speed of the combination is : (a) v cos θ (b) 2v cos θ (c) 3 v cos θ 2 (d) v cos θ 2 2 2. A circular ring of mass 6 kg and radius a is placed such that its centre lies at the origin. Two particles of masses 2 kg each are placed at the intersecting points of the circle with +ve x-axis and +ve y-axis. Then, the angle made by the position vector of centre of mass of entire system with x-axis is : (a) 45o (b) 60o (c) tan–1 æç4ö÷ (d) 30o ç ÷ è5ø 3. A projectile of mass m is fired with velocity v from a point P, as shown. Neglecting air resistance, the magnitude of the change in momentum between the points P and arriving at Q is : mv (a) zero (b) 2 (c) mv (d) 2 mv 4. If the KE of a body is increased by 300 %, its momentum will increase by : (a) 100 % (b) 150 % (d) 175 % 5. A block of mass m moving at speed v collides with another block of mass 3 m at rest. The lighter blocks comes to rest of far collision. The coefficient of restitution is 1 2 1 (a) 2 (b) 3 (c) 4 (d) None 6. A metal ball from a height of 32 m on a steel plate. If the coefficient of restitution is 0.5, to what height will the ball rise after second bounce ? (a) 2 m (b) 4 m (c) 8 m (d) 16 m 7. A mass of 10 g moving horizontally with a velocity of 100 cm/s strikes a pendulum bob of mass 10 g. Length of string is 50 cm. The two masses stick together. The maximum height reached by the system now is : (g = 10 m/s2) PHYSICS Topic: CENTRE OF MASS, CONSERVATION OF MOMENTUM, COLLISION Date: (a) 7.5 cm (b) 5 cm (c) 2.5 cm (d) 1.25 cm 8. A block of mass m is pushed towards a movable wedge of mass nm and height h, with a velocity u. All surfaces are smooth. The minimum value of u for which the block reach the top of the wedge is : (a) (b) 9. At high altitude, a body explodes at rest into two equal fragments with one fragment receiving horizontal velocity of 10 m/s. Time taken by the two radius vectors connecting point of explosion to fragments to make 90o is : (g = 10 m/s2) (a) 10 s (b) 4 s (c) 2 s (d) 1 s 10. A ball thrown with velocity 30 m/s and making an angle 37o with horizontal. The ball strikes a vertical wall at a distance of 12 m from the point of projection and coefficient of restitution between wall and the ball is equal to 0.5. What is the velocity of the ball just after impact on the wall ? (a) 17.7 m/s (b) 15.6 m/s (c) 20.4 m/s (d) 19.4 m/s PHYSICS Topic: CENTRE OF MASS, CONSERVATION OF MOMENTUM, COLLISION Date: Answer Key 1. (a) 2. (a) 3. (c) 4. (a) 5. (d) 6. (a) 7. (d) 8. (c) 9. (c) 10. (a)