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Force needed to pull a block up an incline.

by garfiegrl
Tags: block, force, incline, pull
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garfiegrl
#1
Sep30-09, 03:13 PM
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 [tex]\vartheta[/tex]
WT= w sin [tex]\vartheta[/tex]
[tex]\mu[/tex]s= tan[tex]\vartheta[/tex]

3. The attempt at a solution

I don't even know how to get started.
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Kurdt
#2
Sep30-09, 07:38 PM
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P: 4,982
If the block is moving at a constant speed then you know that there is no net force acting on the block.
garfiegrl
#3
Sep30-09, 08:56 PM
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?

Kurdt
#4
Oct1-09, 05:31 AM
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P: 4,982
Force needed to pull a block up an incline.

So what force is needed to make them balance?
garfiegrl
#5
Oct1-09, 08:26 AM
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?
Kurdt
#6
Oct2-09, 07:22 AM
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What direction will the friction be acting in if the box is being pulled up the slope?
mukundpa
#7
Oct2-09, 07:49 AM
HW Helper
P: 507
What is the direction of the force applied and whether the friction will depend on that direction.
mukundpa
#8
Oct2-09, 07:57 AM
HW Helper
P: 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.


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