EBK COLLEGE PHYSICS
2nd Edition
ISBN: 9780134605500
Author: ETKINA
Publisher: PEARSON CO
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Textbook Question
Chapter 7, Problem 91RPP
BIO Kangaroo hopping Hopping is an efficient method of locomotion for the kangaroo (see Figure 7.18). When the kangaroo is in the air, the Earth-kangaroo system has a combination of gravitational potential energy and kinetic energy. When the kangaroo lands, its Achilles tendons and the attached muscles stretch-a form of elastic potential energy. This elastic potential energy is used along with additional muscle tension to launch the kangaroo off the ground for the next hop. In the red kangaroo, more than 50% of the total energy used during each hop is recovered elastic potential energy. This is so efficient that the kangaroo’s
The horizontal and vertical force components exerted by a firm surface on a kangaroo’s feet while it hops are shown in Figure 7.19a. the vertical force NS on k y (Figure 7.19b) varies: when the kangaroo is not touching the surface S, the force is zero; when it is pushing off, the force is about three times the gravitational force that Earth exerts on the kangaroo. The surface exerts a backward horizontal force (FS on K z) on the kangaroo’s foot while it lands and a forward horizontal force as it pushes off for the next hop (Figure 7.19c), similar to what happens to a human foot when landing in front of the body and when pushing off for another step when behind the body.
Which answer below is closest to the vertical impulse that the ground exerts on the kangaroo while it takes off?
a. 0
b. +50 N.s
c. +150 N.s
d. -50 N.s
e. -150 N.s
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Chapter 7 Solutions
EBK COLLEGE PHYSICS
Ch. 7 - Review Question 7.1 Assuming that Earths orbit...Ch. 7 - Review Question 7.2 A system can possess energy...Ch. 7 - Review Question 7.3 When we use the work-energy...Ch. 7 - Review Question 7.4 If the magnitude of the force...Ch. 7 - Review Question 7.5 Why, when friction cannot be...Ch. 7 - Review Question 7.6 What would change in the...Ch. 7 - Review Question 7.7 Imagine that a collision...Ch. 7 - Review Question 7.8 Toyota says that the power of...Ch. 7 - Review Question 7.9 In this section you read that...Ch. 7 - In which of the following is positive work done by...
Ch. 7 - 2. Which answer best represents the system’s...Ch. 7 - An Atwood machine is shown in Figure Q7.3. As the...Ch. 7 - Prob. 4MCQCh. 7 - 5. Three processes are described below. Choose one...Ch. 7 - 6. Choose which statement describes a process in...Ch. 7 - 7. Which example(s) below involve(s) zero physics...Ch. 7 - 8. Estimate the change in gravitational potential...Ch. 7 - What does it mean if object 1 does +10 J of work...Ch. 7 - You pull on a spring, which obeys Hookes law, in...Ch. 7 - The graph in Figure Q7.11 shows the time...Ch. 7 - 12. A 1400-kg car is traveling on a level road at...Ch. 7 - Prob. 13MCQCh. 7 - Two clay balls are moving toward each other. The...Ch. 7 - 15. Is energy a physical phenomenon, a model, or a...Ch. 7 - 16. Your friend thinks that the escape speed...Ch. 7 - Suggest how you can measure the following...Ch. 7 - How can satellites stay in orbit without any jet...Ch. 7 - Why does the Moon have no atmosphere, but Earth...Ch. 7 - What will happen to Earth if our Sun becomes a...Ch. 7 - 21. In the equation , the gravitational potential...Ch. 7 - 22. You push a small cart by exerting a constant...Ch. 7 - 1. Jay fills a wagon with sand (about 20 kg) and...Ch. 7 - 2. You have a 15-kg suitcase and (a) slowly lift...Ch. 7 - * You use a rope to slowly pull a sled and its...Ch. 7 - A rope attached to a truck pulls a 180-kg...Ch. 7 - 5. You lift a 25-kg child 0.80 m, slowly carry him...Ch. 7 - A truck runs into a pile of sand, moving 0.80 m as...Ch. 7 - 7. A 0.50-kg block is placed in a straight gutter...Ch. 7 - s up a smooth incline, which makes an angle with...Ch. 7 - 9. ** It is a windy day. You are moving a 20-kg...Ch. 7 - A 5.0-kg rabbit and a 12-kg Irish setter have the...Ch. 7 - Prob. 11PCh. 7 - * A pickup truck (2268 kg) and a compact car (1100...Ch. 7 - * When does the kinetic energy of a car change...Ch. 7 - * When exiting the highway, a 1100-kg car is...Ch. 7 - Prob. 15PCh. 7 - 16. * Flea jump flea pushes off a surface by...Ch. 7 - * Roller coaster ride A roller coaster car drops a...Ch. 7 - 18. * BIO EST Heart pumps blood The heart does...Ch. 7 - 19. * Wind energy Air circulates across Earth in...Ch. 7 - 20. * BIO Bone break The tibia bone in the lower...Ch. 7 - 21. * BIO EST Climbing Mt. Everest In 1953 Sir...Ch. 7 - 22. A door spring is difficult to stretch. (a)...Ch. 7 - * A moving car has 40,000 J of kinetic energy...Ch. 7 - 24. * The force required to stretch a slingshot by...Ch. 7 - Jim is driving a 2268-kg pickup truck at 20 m/s...Ch. 7 - 26. * A car skids 18 m on a level road while...Ch. 7 - s mass is m. An average friction force of...Ch. 7 - Prob. 28PCh. 7 - Prob. 29PCh. 7 - 30. In a popular new hockey game, the players use...Ch. 7 - 31. The top of a descending ski slope is 50 m...Ch. 7 - * If 20% of the gravitational potential energy...Ch. 7 - Prob. 33PCh. 7 - 34. A driver loses control of a car, drives off an...Ch. 7 - * You are pulling a box so it moves at increasing...Ch. 7 - s speed increases from zero to 4.0 m/s in a...Ch. 7 - 37. ** EST Hit by a hailstone A 0.030-kg hailstone...Ch. 7 - 38. * BIO Froghopper jump Froghoppers may be the...Ch. 7 - 39. * Bar chart Jeopardy 1 Describe in words and...Ch. 7 - * Bar chart Jeopardy 2 Describe in words and with...Ch. 7 - 41. * Equation Jeopardy 1 Construct a qualitative...Ch. 7 - * Equation Jeopardy 2 Construct a qualitative...Ch. 7 - Prob. 43PCh. 7 - 44. * Evaluation 2 Your friend provides a solution...Ch. 7 - 45. A crab climbs up a vertical rock with a...Ch. 7 - 46 * Work-energy bar charts for a person going...Ch. 7 - Prob. 47PCh. 7 - * A 1060-kg car moving west at 16 m/s collides...Ch. 7 - * You fire an 80-g arrow so that it is moving at...Ch. 7 - 50. * You fire a 50-g arrow that moves at an...Ch. 7 - * To confirm the results of Problem 7.50, you try...Ch. 7 - 52. * Somebody tells you that Figure P7.52 shows...Ch. 7 - 54. A roofing shingle elevator is lifting a...Ch. 7 - 55. (a) What is the power involved in lifting a...Ch. 7 - * A fire engine must lift 30 kg of water a...Ch. 7 - * BIO Internal energy change while biking You set...Ch. 7 - * Climbing Mt. Mitchell An 82-kg hiker climbs to...Ch. 7 - * BIO EST Sears stair climb The fastest time for...Ch. 7 - * BIO EST Exercising so you can eat ice cream You...Ch. 7 - 61. ** BIO Salmon move upstream In the past,...Ch. 7 - * EST Estimate the maximum horsepower of the...Ch. 7 - Prob. 63PCh. 7 - At what distance from Earth is the gravitational...Ch. 7 -
65. * Possible escape of different air molecule...Ch. 7 - Determine the escape speed for a rocket to leave...Ch. 7 - Determine the escape speed for an object to leave...Ch. 7 - If the Sun were to become a black hole, how much...Ch. 7 - * A satellite moves in elliptical orbit around...Ch. 7 - 70. * Determine the maximum radius Earth's Moon...Ch. 7 - 71. You throw a clay ball vertically upward. The...Ch. 7 - Prob. 72GPCh. 7 - Prob. 73GPCh. 7 - 74 * EST A “gravity force car” is powered by the...Ch. 7 - * Loop the loop You are given a loop raceway for...Ch. 7 - 76. ** Atwood machine Two blocks of masses hang...Ch. 7 - andm2 are connected with a string that passes over...Ch. 7 - of all species became extinct, ending the reign of...Ch. 7 - s cradle is a toy that consists of several metal...Ch. 7 - 81. ** Six Flags roller coaster A loop-the-loop on...Ch. 7 - ** Designing a ride You are asked to help design a...Ch. 7 - BIO Metabolic rate Energy for our activities is...Ch. 7 - BIO Metabolic rate Energy for our activities is...Ch. 7 - BIO Metabolic rate Energy for our activities is...Ch. 7 - BIO Metabolic rate Energy for our activities is...Ch. 7 - BIO Metabolic rate Energy for our activities is...Ch. 7 -
BIO Kangaroo hopping Hopping is an efficient...Ch. 7 - BIO Kangaroo hopping Hopping is an efficient...Ch. 7 - BIO Kangaroo hopping Hopping is an efficient...Ch. 7 - BIO Kangaroo hopping Hopping is an efficient...Ch. 7 - BIO Kangaroo hopping Hopping is an efficient...Ch. 7 - BIO Kangaroo hopping Hopping is an efficient...
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