College Physics
2nd Edition
ISBN: 9780134601823
Author: ETKINA, Eugenia, Planinšič, G. (gorazd), Van Heuvelen, Alan
Publisher: Pearson,
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Textbook Question
Chapter 7, Problem 21CQ
In the equation
, the gravitational potential energy is directly proportional to the distance of the object from a planet. In the equation
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We are now able to define a mathematical formula for gravitational potential energy.
Near the Earth's surface, the gravitational potential energy of a system consisting of the earth and an object with a mass m is
EP = mgh,
where g is the acceleration of gravity (9.80 m/s2) and h is the height above ground level (positive upward).
Note that the "ground level" could really be any height we choose, because what's really important is the change in potential energy. The difference between two heights always gives the same change in potential energy, regardless of where we set the "zero" of height. In other words, if we find the change in potential energy
ΔEP = EP,f − EP,i,
the final potential energy minus the initial, we have
ΔEP = mghf − mghi = mgΔh.
The change in gravitational potential energy is just mg times the change in height.
Let's return to our ball-Earth example, only now let's examine a case where a ball is rising in the air.
You toss a ball with a mass of 0.703 kg upward.…
If a particle is moving, it has kinetic energy. Kinetic energy is the energy of motion, and it depends on the speed and mass of the particle. It is given by the formula
Ek = 1/2*mv2,
where
Ek
is the kinetic energy, m is the mass, and v is the speed of the particle.
The formula for kinetic energy has some important features to keep in mind.
Kinetic energy, and every other type of energy as well, is a scalar quantity, given by only a single number. Energy does not have a "direction", unlike a vector quantity. (This is in contrast to the vector quantity momentum, which you might have already studied.)
Kinetic energy, in particular, is always a positive number. (Note the speed v is the magnitude of the vector velocity, and therefore is positive. But even if it were a negative number, squaring it would always lead to a positive result.)
Kinetic energy depends on the square of the speed. (This is in contrast to the magnitude of momentum, mv, a quantity you may have already studied, which…
You have an object of mass 555 kg, that is a distance 1.0 m above the ground. If we
call the ground a height 0, what is the gravitational potential energy of the object
(measured in Joules)?
Your Answer:
Answer
Chapter 7 Solutions
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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