Calculate the acceleration of the block

  • Thread starter raman911
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  • #1
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A 0.5 kg block is being slid up a chalkboard with an applied force of 6.0 N upward and 2.0 N inward towards the board. If the coefficient of kinetic friction is 0.4.

a) Calculate the force of friction.

b) Calculate the acceleration of the block.


F = mju R [ F = u R]

1. F/u = 6/0.4 = 15N ???

2. F = ma ..... 6/0.5 = a = 12m/s^2

not sure... some1 back me up on this!
 
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Answers and Replies

  • #2
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no one helping
 
  • #3
Doc Al
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If you would like help, show what you've done so far--per PF rules.

Start by identifying all the forces acting on the block.
 
  • #4
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If you would like help, show what you've done so far--per PF rules.

Start by identifying all the forces acting on the block.
F = mju R [ F = u R]

1. F/u = 6/0.4 = 15N ???

2. F = ma ..... 6/0.5 = a = 12m/s^2

not sure... some1 back me up on this!
 
  • #5
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Show us your attempts at solving this problem first.
 
  • #6
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Show us your attempts at solving this problem first.
2. (6-(2*0.4))/0.5= 10.4 upwards w.r.t board.

(6-(2*0.4)-(0.5*9.8))/0.5=0.6 upwards w.r.t ground.
 
  • #7
Doc Al
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F = mju R [ F = u R]
I assume F is the friction force? So what is R?
 
  • #8
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I assume F is the friction force? So what is R?
sorry
mean Fn
 
  • #9
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If you would like help, show what you've done so far--per PF rules.

Start by identifying all the forces acting on the block.
can u help now
 
  • #10
Doc Al
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Seems like you have several versions of solutions. Approach it systematically: What forces act on the block? What's the force of friction?
 
  • #11
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Seems like you have several versions of solutions. Approach it systematically: What forces act on the block? What's the force of friction?
can u help me
which formula i need to use first one
 
  • #12
hage567
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For (1), use the formula you've already stated, F=uN. Do you know what force N is in this case? (I think you were calling in R in your first post)
 
  • #13
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For (1), use the formula you've already stated, F=uN. Do you know what force N is in this case? (I think you were calling in R in your first post)
I AM NOT SURE
CAN U DO THAT.
 
  • #14
hage567
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N is the normal force. The block is being pushed against a vertical wall. So which of the two forces you were given in the question is holding the block on the wall? That is the force you need to use to find the force of friction.
 
  • #15
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N is the normal force. The block is being pushed against a vertical wall. So which of the two forces you were given in the question is holding the block on the wall? That is the force you need to use to find the force of friction.
i need help in B
 
  • #16
Doc Al
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i need help in B
So you have finished A and correctly calculated the force of friction? If so, good.

To solve B, identify all the forces acting on the block. Then find the net force and use that to calculate the acceleration via Newton's 2nd law.
 

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