Help with Friction: Solving a Problem Example

[FocusedWolf]

Ok, before i start i'd like to say I'm totally confussed about how to use use the friction formulas in my book...i say this because all my answers are wrong!

Ok so what i need is help in the form of examples...and a lot...cause my book doesn't offer anything.

Anyhoo, heres's a problem I'm trying to solve: ( i rounded off the numbers for clarity)

A block is at rest on an incline 30 degrees.

weight 10kg
Us .50
Uk .40

What is the frictional forces acting on the the 10kg mass. Answer in units of N

Someone help clarify a plan of attack...in meantime I am going to try reading this chapter some more.

 

[Andrew Mason]

A block is at rest on an incline 30 degrees.

weight 10kg
Us .50
Uk .40

What is the frictional forces acting on the the 10kg mass. Answer in units of

First find the normal force. In this case it is equal and opposite to the component of gravity that is perpendicular to the surface of the inclined plane. That will enable you to find the possible kinetic and static friction forces.

Then find the component of gravity along the surface of the inclined plane. That will tell you whether the block moves.

From that you can answer the question.

AM

 

[wais]

Hi there,

I can understand your confusion with using friction formulas. It can definitely be tricky at first, but with practice and examples, you will get the hang of it.

Let's take a look at the problem you provided. The first step in solving any problem involving friction is to identify the forces acting on the object. In this case, we have the weight of the block (10kg) acting downwards and the force of friction acting in the opposite direction, parallel to the incline.

Next, we need to determine the normal force, which is the force perpendicular to the surface of the incline. In this case, it would be the component of the weight that is perpendicular to the incline. We can use trigonometry to find this value. Since the incline is at 30 degrees, the normal force would be equal to 10kg multiplied by the cosine of 30 degrees, which is approximately 8.66kg.

Now, we can use the formula for friction force, which is Ff = μN, where μ is the coefficient of friction and N is the normal force. In this case, we have two coefficients of friction - one for static friction (Us) and one for kinetic friction (Uk). Since the block is at rest on the incline, we will use the coefficient of static friction, which is 0.50. So the friction force would be 0.50 multiplied by 8.66kg, which gives us 4.33kg.

However, the units for force are in Newtons (N), not kilograms (kg). To convert from kg to N, we need to multiply by the acceleration due to gravity (g), which is approximately 9.8 m/s^2. So the final answer would be 4.33kg x 9.8 m/s^2 = 42.45N.

I hope this helps clarify the problem and gives you an idea of how to approach friction problems. Remember to always identify the forces, use the appropriate coefficient of friction, and convert units if necessary. Keep practicing and you'll become more comfortable with using friction formulas. Best of luck!