Frictional Force vs normal force

AI Thread Summary
A 10 N horizontal force is applied to a 50 N block on a rough surface, with static and kinetic friction coefficients of 0.5 and 0.4, respectively. The frictional force is determined by the static friction equation, which states that it is not always equal to the coefficient times the normal force. Since the applied force of 10 N does not exceed the maximum static friction force (25 N), the block remains in static equilibrium. Therefore, the frictional force equals the applied force of 10 N, preventing the block from sliding. Understanding the relationship between applied force and frictional force is crucial in static friction scenarios.
Dalip Saini
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Homework Statement


A 10 N horizontal force is applied to a 50 N block initially at rest on a rough horizontal surface. If the coefficient of static friction is 0.5 and the coefficient of kinetic friction is 0.4, then the frictional force on the block is
  • A

    10 N
  • B

    20 N
  • C
  • 0 N


  • D

  • 25 N

Homework Equations


Frictional force = (coefficent of static friction)(normal force)
Normal Force = mass x gravity = 50 N due to Newtons second law

The Attempt at a Solution


Frictional force = 50 * 0.4 = 20 N but the answer is 10 N and I don't understand why
 
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With regard to static friction, the frictional force is not always equal to the coefficient of static friction times the normal force. If the frictional force does not exceed (coefficient of static friction)(normal force), then the object will not slide on the surface. In your case it doesn't, so no sliding will occur, and the body will be in static equilibrium, with the frictional force being in equilibrium with the 10 N applied force. In general, for static friction,

(frictional force) ≤ (coefficient of friction)(normal force)Chet
 
Chestermiller said:
With regard to static friction, the frictional force is not always equal to the coefficient of static friction times the normal force. If the frictional force does not exceed (coefficient of static friction)(normal force), then the object will not slide on the surface. In your case it doesn't, so no sliding will occur, and the body will be in static equilibrium, with the frictional force being in equilibrium with the 10 N applied force. In general, for static friction,

(frictional force) ≤ (coefficient of friction)(normal force)Chet
okay thank you so much
 

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