Force needed to pull a block up an incline.

  • Thread starter garfiegrl
  • Start date
  • #1
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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


WN= w cos [tex]\vartheta[/tex]
WT= w sin [tex]\vartheta[/tex]
[tex]\mu[/tex]s= tan[tex]\vartheta[/tex]

The Attempt at a Solution



I don't even know how to get started.
 

Answers and Replies

  • #2
Kurdt
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If the block is moving at a constant speed then you know that there is no net force acting on the block.
 
Last edited:
  • #3
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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
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So what force is needed to make them balance?
 
  • #5
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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
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What direction will the friction be acting in if the box is being pulled up the slope?
 
  • #7
mukundpa
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What is the direction of the force applied and whether the friction will depend on that direction.
 
  • #8
mukundpa
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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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