Force needed to pull a block up an incline.

by garfiegrl
Tags: block, force, incline, pull
 P: 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.
 PF Patron Sci Advisor Emeritus P: 4,974 If the block is moving at a constant speed then you know that there is no net force acting on the block.
 P: 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?
PF Patron
Emeritus
P: 4,974

Force needed to pull a block up an incline.

So what force is needed to make them balance?
 P: 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?
 PF Patron Sci Advisor Emeritus P: 4,974 What direction will the friction be acting in if the box is being pulled up the slope?
 HW Helper P: 508 What is the direction of the force applied and whether the friction will depend on that direction.
 HW Helper P: 508 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.

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