Additional Problems 9. Erika is on an elevator and presses the 14. A 7.25-g bullet is fired from a gun. The button to go down. When the elevator muzzle velocity of the bullet is 223 m/s. first starts moving, it has an acceleration of Assume that the bullet accelerates at a 2.5 m/s2 downward. Erika and the elevator constant rate along the barrel of the gun have a combined mass of 1250 kg. before it emerges with constant speed. a. Draw a free-body diagram for the The barrel of the gun is 0.203 m long. elevator. What average force does the bullet exert b. What is the tension in the cable that on the gun? provides the upward force on the 15. A 15.2-kg police battering ram exerts an elevator car? average force of 125 N on a 10.0-kg door. a. What is the average acceleration of the 10. Ngan has a weight of 314.5 N on Mars and door? a weight of 833.0. N on Earth. b. What is the average acceleration of the a. What is Ngan's mass on Mars? - battering ram? Appendix B b.' What is the acceleration due to gravity 16. As a demonstration, a physics teacher on Mars, 8Mars attaches a 7.5-kg object to the ceiling by a nearly massless string. This object then 11. Alex is on the wrestling team and has a supports a 2.5-kg object below it by anoth- mass. of 85.3 kg. Being a whiz at physics, er piece of string. Finally, another piece of he realizes that he is over the 830.0-N cut- string hangs off the bottom of the lower off for his weight class. If he can convince object to be pulled with ever increasing the trainers to measure his weight in the force until the string breaks somewhere elevator, what must be the acceleration The string will break when the tension of the elevator so that he just makes his reaches 156 N. weight class? a. Which length of string will break first? 12. During a space launch, an astronaut typi- b. What is the maximum downward force cally undergoes an acceleration of 3 gs, the physics teacher can apply before the which means he experiences an accelera- string breaks? tion that is three times that of gravity alone. What would be the apparent weight of a 205-kg astronaut that experiences a 3-8 liftoff? 7.5 kg 2.5 kg 13. Alfonso and Sarah like to go sky diving together. Alfonso has a mass of 88 kg, and Sarah has a mass of 66 kg. While in free fall together, Alfonso pushes Sarah hori- zontally with a force of 12.3 N. 1 . .. a. What is Alfonso's horizontal acceleration? b. What is Sarah's horizontal acceleration? 17. A 10.0-kg object is held up by a string that will break when the tension exceeds 1.00X 102 N. At what upward acceleration will the string break? 864 Appendix BAdditional Problems 3. Draw a free-body diagram for a submerged 7. Two dogs fight over a bone. The larger of beach ball as it rises toward the surface just the two pulls on the bone to the right with after being released. Identify the forces act- a force of 42 N. The smaller one pulls to ing on the beach ball and indicate the direc- the left with a force of 35 N. tion of the net force and the acceleration. a. Draw the free-body diagram for the bone b. What is the net force acting on the bone? c. If the bone has a mass of 2.5 kg, what is its acceleration? Additional Problems 4. Muturi is rearranging some furniture. He pushes the dresser with a force of 143 N, and there is opposing frictional force of Dog 1 Dog 2 112 N. What is the net force? 5. One of the floats in a Thanksgiving Day parade requires four people pulling on ropes to maintain a constant speed of 8. A large model rocket engine can produce 3.0 km/h for the float. Two people pull a thrust of 12.0 N upon ignition. This with a force of 210 N each, and the other engine is part of a rocket with a total mass two pull with a force of 140 N each. of 0.288 kg when launched. a. Draw a free-body diagram. a. Draw a free-body diagram of the rocket b. What is the force of friction between just after launch. the float and the ground? b. What is the net force that is acting on the model rocket just after it leaves the ground? c. What is the initial acceleration of the rocket? 6. Five people are playing tug-of-war. Anders and Alyson pull to the right with 45 N and 35 N, respectively. Calid and Marisol pull to the left with 53 N and 38 N, respectively. With what force and in what direction does Benito pull if the game is tied? Appendix B 863