Two questions, work-kinetic energy related

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SUMMARY

The discussion addresses two physics problems related to work and kinetic energy. The first problem involves a 5.0-kg block sliding down a 30-degree incline with a coefficient of kinetic friction of 0.25, requiring the calculation of the friction force's work at a speed of 3.0 m/s. The second problem involves a 2.0-kg block sliding down a frictionless incline with an external force of 3.0 N, determining the kinetic energy at point B given an initial kinetic energy of 10 J at point A, which is 2.0 m apart. Participants express difficulty in obtaining correct answers using the equations for work and kinetic energy.

PREREQUISITES
  • Understanding of Newton's laws of motion
  • Knowledge of work-energy principle
  • Familiarity with kinetic friction calculations
  • Basic concepts of kinetic energy and its equations
NEXT STEPS
  • Review the work-energy principle and its applications in physics problems
  • Study the calculations for friction force using the formula Fk = μk * N
  • Explore the concept of net work done on an object and its impact on kinetic energy
  • Practice solving problems involving inclined planes and external forces
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Students studying physics, particularly those focusing on mechanics, as well as educators looking for examples of work and energy problems in a classroom setting.

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Homework Statement



1)A 5.0-kg block slides down a surface inclined 30 degrees with the horizontal. If the coefficient of kinetic friction for the block and the surface is equal to 0.25, at what rate is the friction force on the block doing work at an instant when the speed of the block is 3.0 m/s?


2) Consideran incline with two locations on the slope, A and B. point A on the incline does not necessarily occur at the top of the incline but does occur before B.
A 2.0-kg block slides down a frictionless incline from p.A to p.B. A force (magnitude P = 3.0 N) acts on the block between A and B, as shown. Points A and B are 2.0 m apart. If the kinetic energy of the block at A is 10 J, what is the kinetic energy of the block at B?

Homework Equations





The Attempt at a Solution


i keep getting incorrect numbers (the questions are multiple choice).
 
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For the first one I used P=Fk and W=F*Δx but i dont know what i'm doing wrong. For the second one, i used KEf=KEi+WAB but again, wrong answer. Please help!
 

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