Force needed to pull a block up an incline.

[garfiegrl]

Homework Statement

Calculate the force needed to pull a mass of 20 kg at a uniform slow speed up a plane inclined at an angle of 30 with the horizontal if the coefficient of kinetic friction is 0.20.

Homework Equations

W_N= w cos $$\vartheta$$
W_T= w sin $$\vartheta$$
$$\mu$$_s= tan$$\vartheta$$

The Attempt at a Solution

I don't even know how to get started.

 

[Kurdt]

If the block is moving at a constant speed then you know that there is no net force acting on the block.

 

[garfiegrl]

so the friction force is
(.2)(20)(9.8)(cos 30) ?

and the gravitational force is
(20)(9.8)(sin 30) ?

i got 34 N for friction and 98 N for gravitational.

are they supposed to equal zero? or do i add them together to find the force i need to overcome? or could i just overcome the strongest?

 

[Kurdt]

So what force is needed to make them balance?

 

[garfiegrl]

okay, so 34 N for friction pull the box up the slope, and 98 N gravity pull down.

98 N - 34 N = 64 N needed to equalize them, and more than 64 to make it move uphill?

 

[Kurdt]

What direction will the friction be acting in if the box is being pulled up the slope?

 

[mukundpa]

What is the direction of the force applied and whether the friction will depend on that direction.

 

[mukundpa]

If the minimum force needed is required than the force must be applied at an angle equal to angle of friction [tan^-1 (u)] with the incline.