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Questions 281 1. Does a large force always produce a larger impulse on an object than a smaller force does? Explain. 2. If the speed of a particle is doubled, by what factor is its momentum changed? By what factor is its kinetic energy If two particles have equal kinetic energies, are their mo- menta necessarily equal? Explain. 4. While in motion, a pitched baseball carries kinetic energy and momentum. (a) Can we say that it carries a force that 5. An isolated system is initially at rest. Is it possible for parts of the system to be in motion at some later time? If so, ex- 6. If two objects collide and one is initially at rest, is it possi- ble for both to be at rest after the collision? Is it possible Explain how linear momentum is conserved when a ball bounces from a floor. 8. A bomb, initially at rest, explodes into several pieces. (a) Is linear momentum of the system conserved? (b) Is kinetic 9. A ball of clay is thrown against a brick wall. The clay stops and sticks to the wall. Is the principle of conservation of 10. You are standing perfectly still, and then you take a step forward. Before the step your momentum was zero, but af- 11. When a ball rolls down an incline, its linear momentum in- creases. Is the principle of conservation of momentum vio- 7. 3. 12. Consider a perfectly inelastic collision between a car and a large truck. Which vehicle experiences a larger change in A sharpshooter fires a rifle while standing with the butt of the gun against his shoulder. If the forward momentum of a 14. A pole-vaulter falls from a height of 6.0 m onto a foam rub- ber pad. Can you calculate his speed just before he 15. Firefighters must apply large forces to hold a fire hose steady (Fig. Q9.15). What factors related to the projection 13. Figure Q9.15 © Bill Stormont/The Stock Market Q U E S T I O N S The position vector of the center of mass of an extended object can be obtained from the integral expression (9.33) The velocity of the center of mass for a system of particles is (9.34) The total momentum of a system of particles equals the total mass multiplied by the ve- Newton’s second law applied to a system of particles is (9.38) where a CM is the acceleration of the center of mass and the sum is over all external forces. The center of mass moves like an imaginary particle of mass M under the influ- " F ext ! M a CM v CM ! " i m i v i M r CM ! 1 M
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dm 16. A large bed sheet is held vertically by two students. A third student, who happens to be the star pitcher on the base- |