Static friction force homework

In summary, the conversation discusses a question about an object at rest on a surface with a static coefficient of friction of 0.6. The question asks how quickly the object will move if pushed with a force of 27N. The given solution states that the object will not move due to the maximum friction force being equal to the pushing force. However, the participant notes a possible typo in the question regarding the weight of the object and provides a calculation for the normal force and maximum friction force.
  • #1
generalguiness
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Homework Statement


A 50kg object begins at rest on a surface with a static coef of friction at 0.6. If you push horizontally on the object with a force of 27N, how quickly will it move across the surface?

Homework Equations



The Attempt at a Solution

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This is from Trivium Praxis test prep book. The solution given is 0.6*50=30N of static friction, so no, it will not move. In the very brief section explaining friction, it said that friction=coef * normal force, but they labelled it as capitol N. Shouldnt the normal force be 50g? So F=0.6 * 50g? I decided to try to pass the test this summer after taking physics 15+ years ago!
 
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  • #2
There's likely a typo in the question. The object description was probably meant to give its weight as 50 Newtons, not mass in kilograms.
 
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  • #3
Welcome to Physics Forums.
Are you sure it is a 50 kg object, and not a 50 Newton object?
But assuming it is a 50 kg object: If it is a horizontal surface, the normal force N will be equal to the weight of the object. The weight is mg = (50 kg)(9.8 m/s^2) = 490 N (where N is Newtons)
So the normal force will be N = 490 N. And the maximum friction force will be f = μN = (0.6)(490) = 294 N. So if you push with 27 N, the friction force will also be 27 N. Thus the object will not move.
 
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Thanks. This is the 2nd error I think I've found and I've only done 12 questions in of the first section!
 

1. What is static friction force?

Static friction force is a force that acts between two surfaces in contact with each other and prevents them from sliding against each other when there is no relative motion between them.

2. How is static friction force different from kinetic friction force?

Static friction force only occurs when there is no relative motion between the two surfaces, while kinetic friction force occurs when there is relative motion between the two surfaces.

3. What factors affect the magnitude of static friction force?

The magnitude of static friction force depends on the type of surfaces in contact, the normal force acting between the surfaces, and the roughness of the surfaces.

4. How do you calculate the value of static friction force?

The value of static friction force can be calculated using the equation Fs = μsN, where Fs is the static friction force, μs is the coefficient of static friction, and N is the normal force.

5. How can static friction force be reduced?

Static friction force can be reduced by using lubricants between the surfaces, increasing the surface area of contact, or reducing the normal force acting between the surfaces.

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