# Force needed to pull a block up an incline.

1. ### garfiegrl

14
1. The problem statement, all variables and given/known data
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.

2. Relevant equations
WN= w cos $$\vartheta$$
WT= w sin $$\vartheta$$
$$\mu$$s= tan$$\vartheta$$

3. The attempt at a solution

I don't even know how to get started.

2. ### Kurdt

4,941
Staff Emeritus
If the block is moving at a constant speed then you know that there is no net force acting on the block.

Last edited: Oct 2, 2009
3. ### garfiegrl

14
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?

4. ### Kurdt

4,941
Staff Emeritus
So what force is needed to make them balance?

5. ### garfiegrl

14
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?

6. ### Kurdt

4,941
Staff Emeritus
What direction will the friction be acting in if the box is being pulled up the slope?

7. ### mukundpa

507
What is the direction of the force applied and whether the friction will depend on that direction.

8. ### mukundpa

507
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.