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An electron strikes on a macroscopic target and recoils back. A closer look shows the electron to scatter backward after interacting with the proton.
A subatomic particle scatters straight backward from a target particle. In experiments seeking evidence for quarks, electrons were observed to occasionally scatter straight backward from a proton.

Section summary

  • The conservation of momentum principle is written
    p tot = constant size 12{p rSub { size 8{"tot"} } ="constant"} {}
    or
    p tot = p tot ( isolated system ) , size 12{p rSub { size 8{"tot"} } =p' rSub { size 8{"tot"} } ````` \( "isolated system" \) ,} {}
    p tot size 12{p rSub { size 8{"tot"} } } {} is the initial total momentum and p tot size 12{ ital "p'" rSub { size 8{"tot"} } } {} is the total momentum some time later.
  • An isolated system is defined to be one for which the net external force is zero F net = 0 . size 12{ left (F rSub { size 8{ ital "net"} } =0 right ) "." } {}
  • During projectile motion and where air resistance is negligible, momentum is conserved in the horizontal direction because horizontal forces are zero.
  • Conservation of momentum applies only when the net external force is zero.
  • The conservation of momentum principle is valid when considering systems of particles.

Conceptual questions

Professional Application

If you dive into water, you reach greater depths than if you do a belly flop. Explain this difference in depth using the concept of conservation of energy. Explain this difference in depth using what you have learned in this chapter.

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Under what circumstances is momentum conserved?

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Can momentum be conserved for a system if there are external forces acting on the system? If so, under what conditions? If not, why not?

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Momentum for a system can be conserved in one direction while not being conserved in another. What is the angle between the directions? Give an example.

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Professional Application

Explain in terms of momentum and Newton’s laws how a car’s air resistance is due in part to the fact that it pushes air in its direction of motion.

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Can objects in a system have momentum while the momentum of the system is zero? Explain your answer.

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Must the total energy of a system be conserved whenever its momentum is conserved? Explain why or why not.

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Problems&Exercises

Professional Application

Train cars are coupled together by being bumped into one another. Suppose two loaded train cars are moving toward one another, the first having a mass of 150,000 kg and a velocity of 0.300 m/s, and the second having a mass of 110,000 kg and a velocity of 0 . 120 m/s size 12{ - 0 "." "120"`"m/s"} {} . (The minus indicates direction of motion.) What is their final velocity?

0.122 m/s

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Suppose a clay model of a koala bear has a mass of 0.200 kg and slides on ice at a speed of 0.750 m/s. It runs into another clay model, which is initially motionless and has a mass of 0.350 kg. Both being soft clay, they naturally stick together. What is their final velocity?

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Professional Application

Consider the following question: A car moving at 10 m/s crashes into a tree and stops in 0.26 s. Calculate the force the seatbelt exerts on a passenger in the car to bring him to a halt. The mass of the passenger is 70 kg. Would the answer to this question be different if the car with the 70-kg passenger had collided with a car that has a mass equal to and is traveling in the opposite direction and at the same speed? Explain your answer.

In acollision withan identicalcar, momentumis conserved.Afterwards v f = 0 for bothcars. Thechange inmomentum willbe thesame asin thecrash withthe tree.However, theforce onthe bodyis notdetermined sincethe timeis notknown. Apadded stopwill reduceinjurious forceon body.

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What is the velocity of a 900-kg car initially moving at 30.0 m/s, just after it hits a 150-kg deer initially running at 12.0 m/s in the same direction? Assume the deer remains on the car.

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A 1.80-kg falcon catches a 0.650-kg dove from behind in midair. What is their velocity after impact if the falcon’s velocity is initially 28.0 m/s and the dove’s velocity is 7.00 m/s in the same direction?

22.4 m/s in the same direction as the original motion

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Questions & Answers

Discuss the differences between taste and flavor, including how other sensory inputs contribute to our  perception of flavor.
John Reply
taste refers to your understanding of the flavor . while flavor one The other hand is refers to sort of just a blend things.
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While taste primarily relies on our taste buds, flavor involves a complex interplay between taste and aroma
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omeprazole
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Not really sure
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to drain extracellular fluid all over the body.
asegid
The lymphatic system plays several crucial roles in the human body, functioning as a key component of the immune system and contributing to the maintenance of fluid balance. Its main functions include: 1. Immune Response: The lymphatic system produces and transports lymphocytes, which are a type of
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to transport fluids fats proteins and lymphocytes to the blood stream as lymph
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Anatomy is the identification and description of the structures of living things
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Anatomy is the study of the structure of the body, while physiology is the study of the function of the body. Anatomy looks at the body's organs and systems, while physiology looks at how those organs and systems work together to keep the body functioning.
AI-Robot
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Enzymes are proteins that help speed up chemical reactions in our bodies. Enzymes are essential for digestion, liver function and much more. Too much or too little of a certain enzyme can cause health problems
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it is because of the enzyme that the stomach produce that help the stomach from the damaging effect of HCL
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function of digestive
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37 degrees selcius
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37°c
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36.5
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37°c
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the normal temperature is 37°c or 98.6 °Fahrenheit is important for maintaining the homeostasis in the body the body regular this temperature through the process called thermoregulation which involves brain skin muscle and other organ working together to maintain stable internal temperature
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anaemia is the decrease in RBC count hemoglobin count and PVC count
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Organ Systems Of The Human Body (Continued) Organ Systems Of The Human Body (Continued)
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Source:  OpenStax, College physics. OpenStax CNX. Jul 27, 2015 Download for free at http://legacy.cnx.org/content/col11406/1.9
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