Solve Friction Problem: Find Fx, Acceleration

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In summary, the conversation discusses a problem involving a block being pushed on a horizontal floor with a given force and angle. The coefficient of kinetic friction and the normal force are mentioned, and calculations are made to determine the magnitude of the frictional force and the block's acceleration. The conversation also addresses the use of the "Edit" and "Delete" options in a forum.
  • #1
AtlBraves
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I am having trouble with this problem. I found the answer to a to be 14 N, but the online quiz says it is wrong. Fx-f=0. Fcos(theta)-f=0. f=18cos40=14 N. What am I doing wrong?

A 3.5 kg block is pushed along a horizontal floor by a force F of magnitude 18 N at an angle = 40° with the horizontal (Figure 6-20). The coefficient of kinetic friction between the block and floor is 0.25.
(a) Calculate the magnitude of the frictional force on the block from the floor.
(b) Calculate the magnitude of the block's acceleration acceleration.

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  • #2
Welcome to PF!
In order to delete in the other forum, press the "Edit button". On top of that, there's a "Delete" option.
 
  • #3
[tex] F_{x} - F_{f} [/tex] is not 0, It is moving on the x-axis.

Remember

[tex] F_{f} = \mu N [/tex]
 
  • #4
For your problem:
Note that the NORMAL force acting on the block must be GREATER than the weight, due the vertical component of F.
Hence, the frictional force is also greater..
 
  • #5
So if [tex] F_{f} = \mu N,[/tex] then [tex] F_{f} = \mu * (mg+18sin40) = .25 * ((3.5*9.8)+18sin40) = 12 N? [/tex]
 
  • #6
That looks correct, yes.
(Do you understand, to your own satisfaction, why you need that addition to the weight?)
I haven't checked your numbers, though..
 
  • #7
Oops. I mistyped. The correct answer is 11 N I'm hoping. Yes I do now see why the normal force is greater than the weight. Thanks for all of the help.
 
  • #8
Perhaps you shouldn't round down to an integer answer.
 

1. What is friction and why is it important to solve friction problems?

Friction is a force that opposes motion between two surfaces that are in contact. It is important to solve friction problems because it affects the movement and efficiency of objects, and understanding it can help improve designs and prevent accidents.

2. How do you calculate the force of friction (Fx)?

The force of friction (Fx) can be calculated by multiplying the coefficient of friction (μ) by the normal force (N) between the two surfaces. Fx = μN.

3. What is the relationship between friction and acceleration?

Friction opposes motion, so it can act to decrease acceleration. However, in some cases, friction can also help increase acceleration by providing traction and preventing slipping.

4. How do you solve for acceleration in a friction problem?

To solve for acceleration in a friction problem, you need to first calculate the net force acting on the object by adding up all the forces (including friction) and using Newton's second law (F=ma). Then, divide the net force by the mass of the object to find the acceleration.

5. What factors affect the force of friction?

The force of friction depends on the type of surfaces in contact, the coefficient of friction, and the normal force. It can also be affected by factors such as the speed of the object, the presence of lubricants, and the roughness of the surfaces.

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