MOMENTUM AND ITS CONSERVATION Understanding Physics Concepts Circle the letter of the choice that best completes the statement. 1. Impulse equals a. instantaneous momentum c. the difference in the final and initial momentums b. mass times velocity d. the sum of forces acting on a body 2. On a force-time graph, the area under the graph is a measure of_ a. force c. mass b. impulse d. momentum 3. An air bag is effective because it the amount of force by increasing the time interval over which it acts. a. balances c. eliminates b. decreases d. increases 4. The angular momentum of an object equals the product ofthe object's . a. mass and angular velocity c. moment of inertia and linear velocity b. moment of inertia and angular d. momentum and angular velocity velocity 5. The angular impulse-angular momentum theorem states that the angular impulse on an object equals the object's final minus its initial 3. angular momentum c. impulse b. angular velocity d. torque 6. If no torques are acting on an object, its angular momentum is a. constant c. increasing b. decreasing d. zero 7. As Earth orbits the Sun, at its annual point of closest approach, Earth's moment of inertia decreases, causing its speed to a. hold constant I:. increase b. decrease d. remain unaffected 8. Ball A collides with ball B. The force ball A exerts on ball B compared to the force ball 3 exerts on ball A. a. is not equal in magnitude c. is equal in magnitude and opposite in direction b. is less in magnitude and d. is equal in magnitude and acts in the same direction opposite in direction 9. In an isolated system, the net on that system is zero. a. external force c. internal force b. time interval d. displacement 10. In order for momentum to be conserved, the system must be a. both closed and isolated c. closed but not isolated b. either closed or isolated d. isolated but not closed 11. A student on in-line skates is holding onto a grocery cart. She pushes the cart away from her. The resulting backward movement of the skater is an example of a. force c. propulsion b. isolation cl. recoil 12. One billiard ball strikes another billiard ball, and they move away from each other at a 90 angle. The momentums involved include of the velocity before and after the collision. a. only the direction c. the magnitude and direction b. only the magnitude d. the square ofthe magnitude 13. A diverjumping from a board into a pool can move his arms and legs to alter his a. speed c. angular velocity b. direction cl. impulse 14. is conserved if no net torque acts on an object. a. Force c. Moment of inertia b. Angularmomentum d. Impulse 15. To conserve angular momentum, if the axis of rotation and moment of inertia of a spinning object decrease, the of that object increases. a. angular velocity c. net torque b. force d. impulse 16. The precession of a spinning top indicates there is a. a net torque on it, and its c. no net torque on it, and its direction changes direction changes b. a net torque on it, and its d. no net torque on it, and its direction does not direction does not change change 17. If a torque-free object starts with no angular momentum, it must a. continue to rotate downward c. continue to have no angular momentum b. wobble on its pivot point d. rotate in the opposite direction Thinking Critically Write the term that correctly completes the stotemen t. 1. The linear momentum of an object can be calculated by multiplying the mass of the object by its 2. The greatest change in momentum will be produced by a large force acting over a(n) period of time. 3. Impulse can be represented by the mathematical expression 4. When a golf club hits a golf ball, the magnitude of the change in momentum ofthe ball is the magnitude ofthe change in momentum of the club. 5. A system is closed ifthe system does not gain or lose 6. An internal force the total momentum of a closed system. 7. A person is standing on roller blades and is holding a heavy medicine ball. If he throws the ball horizontally to the right, his resulting motion will be 8. Two moving objects collide and move on paths that are 120 apart. The total momentum of the objects after the collision is the total momentum before the collision. 9. Gyroscopes are used to fix direction because they have