Newton's Second Law and Friction

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SUMMARY

The discussion focuses on calculating the horizontal force required to drag block B to the left at constant speed while block A remains at rest. Given the weights of block A (1.14 kg) and block B (3.66 kg), and a coefficient of kinetic friction (μ) of 0.300, the net force equation (Fnet = ma) is applied. The user initially misinterprets the forces in the free body diagrams, particularly the direction of frictional forces acting on both blocks. The correct approach involves balancing the applied force and frictional forces to maintain constant velocity.

PREREQUISITES
  • Understanding of Newton's Second Law (Fnet = ma)
  • Knowledge of frictional forces and coefficients (Ff = μN)
  • Ability to draw and interpret free body diagrams (FBDs)
  • Basic algebra for solving equations
NEXT STEPS
  • Study the application of Newton's Second Law in multi-body systems
  • Learn about the effects of kinetic friction in various scenarios
  • Practice drawing and analyzing free body diagrams for complex systems
  • Explore the relationship between force, mass, and acceleration in real-world applications
USEFUL FOR

Students studying physics, particularly those focusing on mechanics, as well as educators seeking to clarify concepts related to forces and friction in multi-body systems.

am13
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Homework Statement



Block A weighs 1.14 and block B weighs 3.66. Block A rests on top of block B and has a cable connecting it to the wall on its right. The coefficient of kinetic friction between all surfaces is 0.300. Find the magnitude of the horizontal force necessary to drag block B to the left at constant speed if A is held at rest. (See Figure B)

Homework Equations



Fnet = ma
Ff=μN
Fnet = 0

The Attempt at a Solution



I think that I am just getting the forces on the free body diagram wrong. I drew FBDs for block B and block A and got that Fnet = 0, and so the horzontal force plus force friction by block A minus force friction by the ground equals 0. And I got F = FfG-FfA. What have I done wrong?
 

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Hi am13, welcome to PF.
The frictional force acting on A is towards right.
Reaction to this force on B acts towards left.
Applied force on B is towards left.
Frictional force on B acts towards...?
What is the condition for the constant velocity of B?
 

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