Finding Friction with a .26kg Mass at an Angle of 26.1°

[Emily266]

Homework Statement

Draw an F_n picture and find Ff_s.
mass=.26kg
θ=26.1
F_a= 0

Homework Equations

F_ll= mgsinθ
F_net= sum of all forces parallel to ramp
F_net= ma

The Attempt at a Solution

I have the picture drawn but I don't know how to find friction.

 

[Rake-MC]

I assume Ff_s is the static frictional force. Therefore, even though you haven't stated otherwise I'll assume that the system is in static equilibrium (ie. the sum of all forces = 0).

Using this information, show us your summation of all the forces.

 

[Emily266]

Yes, Ff_s was meant to represent static friction. I was unaware that static friction meant that all forces equaled zero.

F_net=0 so F_ll-Ff_s

0=1.144-Ff_a
-1.144=-Ff_a
Ff_a=1.14N

 

[Rake-MC]

If you are given a value for static friction, it does not mean that the sum of forces is zero, I just assumed that considering there is not enough information given (that I can see at least) to solve this question provided the mass has overcome the force of static friction.

Your calculation is ok. Just be aware that most physics questions take acceleration due to gravity to be 9.8 or 9.81 ms^-2, however if you've been using 10ms^-2 consistently in your class, then it's best not to change it now.

 

[Emily266]

Oh, my teacher did not say that the forces were all equal to zero, just that the applied force was equal to zero.
I don't know if this helps, but this is a lab and we were increasing the angle of a ramp until our mass (a piece of wood with a few weights attached) moved down the ramp. Yeah, our teacher likes to round things.