Kinetic Friction problem

  • Thread starter mvpshaq32
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  • #1
mvpshaq32
28
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Homework Statement


The lower block in the figure is pulled on by a rope with a tension force of 20 N. The coefficient of kinetic friction between the lower block and the surface is 0.30. The coefficient of kinetic friction between the lower block and the upper block is also 0.30.
knight_Figure_08_28.jpg


Find the acceleration of the 2.0kg block

Homework Equations





The Attempt at a Solution




I set m1a= T - (0.3)m1g and m2a= 20 - T - 0.3m1+2g. After which I added them and isolating a, giving me a=(20 - 0.3m1+2g - 0.3m1g)/(m1+m2), which gave me the answer 2.75, but apparently it is not correct.

Never mind, I solved it. I forgot the friction between block 1 and 2 for movement of block 2
 
Last edited:

Answers and Replies

  • #2
Vipho
13
1
m1a= T - (0.3)m1g
m2a= 20 - T - 0.3m1+2g-0.3m1g

==>a=[20-(m1+m2)g*0.3-2*0.3*m1g]/(m1+m2)=5/3 (ms^-2)

is it right?
 
  • #3
mvpshaq32
28
0
Yep, you got the equation set up right, but the answer is 1.77, not 5/3
 

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