Kinetic Energy and Work Energy Theorem

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SUMMARY

The discussion focuses on calculating the work done by brakes on a bicyclist and bicycle system, specifically a 65kg rider and an 8.8kg bicycle traveling at 14m/s. The work required to stop the system is calculated using the work-energy theorem, yielding a result of 7232.4 Joules. For determining the distance traveled during braking, participants suggest using kinematic equations, specifically relating average acceleration to velocity and time. The units for work are confirmed to be Joules, clarifying the energy involved in the braking process.

PREREQUISITES
  • Understanding of the work-energy theorem
  • Familiarity with kinetic energy calculations
  • Basic knowledge of kinematic equations
  • Concept of average acceleration
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  • Study the derivation of the work-energy theorem
  • Learn how to apply kinematic equations in real-world scenarios
  • Explore the relationship between force, mass, and acceleration using Newton's second law
  • Investigate the implications of energy conservation in mechanical systems
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Physics students, educators, and anyone interested in understanding the principles of mechanics, particularly in relation to energy, work, and motion dynamics.

just.karl
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A 65kg bicyclist rides his 8.8kg bicycle with a speed of 14m/s. (a) How much work must be done by the brakes to bring the bike and rider to a stop? (b) How far does the bicycle travel if it takes 4.0s to come to rest? (c) What is the magnitude of the braking force?


So for part (a) the equation I would use is W=1/2mv_f^2 - 1/2mv_i^2 correct? Which then I get for an answer is 7232.4=W which means 7232.4 Newtons?

For part (b) I know the work that it takes to stop the bicyclist and bicycle but what I'm confused on what equation I would need to use to figure that out.


thanks
 
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For part (a), work is the change in kinetic energy, which you did good...but what are the units for work? If it is equal to KEf - KEi, what does that tell you?

For part (b), think kinematics.
 
O yeah it's joules for part (a)

For part (b) it would be just velocity/time = -average acceleration then I would just multiply that by the amount of time? correct?
 

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