Find Frictional force on a block

AI Thread Summary
To find the frictional force on a 9 kg block on a 30° incline with a static coefficient of friction of 0.7, the normal force must first be calculated using the gravitational force. The gravitational force is determined by G = mg, where g is -9.81 m/s². The normal force, FN, is equal in magnitude but opposite in direction to G, allowing for the calculation of the frictional force using the equation Ff = μ * FN. The calculated frictional force options provided are 9.36841 N, 76.3834 N, 53.4684 N, 44.1 N, and 30.87 N. The discussion emphasizes understanding the relationship between gravitational and normal forces to solve for friction.
trivk96
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Homework Statement



A block of mass 9 kg rests on a plane inclined
at an angle of 30◦. The static coefficient of
friction between the block and the plane is
0.7.
What is the frictional force on the block?
1. 9.36841 N
2. 76.3834 N
3. 53.4684 N
4. 44.1 N
5. 30.87


Homework Equations


Ff=ma
F=μ*Fn


The Attempt at a Solution


I have no idea
 
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The point here is that FN= |G| , they have the same numerical value (are equally large), but they go in the oppposite directions , thus one is positive, the other is negative, + or - sign.

Since gravity pulls downwards, G, the gravitational force points downwards, N is the normal force (in the opposite direction).If we choose positive direction upwards, gravitational pull is negative. with g=-9,81 m/s^2. Remember G=mg, using that FN= |G| will give you the normal force and you can calculate the frictional force from your information.

trivk96 said:

Homework Statement



A block of mass 9 kg rests on a plane inclined
at an angle of 30◦. The static coefficient of
friction between the block and the plane is
0.7.
What is the frictional force on the block?
1. 9.36841 N
2. 76.3834 N
3. 53.4684 N
4. 44.1 N
5. 30.87


Homework Equations


Ff=ma
F=μ*Fn


The Attempt at a Solution


I have no idea
 

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