# Find Frictional force on a block

1. Oct 4, 2011

### trivk96

1. The problem statement, all variables and given/known data

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

2. Relevant equations
Ff=ma
F=μ*Fn

3. The attempt at a solution
I have no idea

2. Oct 5, 2011

### mstud

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.