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Not sure where i went wrong at

  • #1

Homework Statement


A 1.50 m-long, 480 g rope pulls a 8.00 kg block of ice across a horizontal, frictionless surface. The block accelerates at 2.40 m/s^2. How much force pulls forward on (a) the ice, (b) the rope?


Homework Equations


F=m*a


The Attempt at a Solution


for A i got the right answer by
Acceleration of the block = 2.4 m/s^2
mass of the block = 8kg
Force = 8*2.4 = 19.2 N

but for b i did:
Acceleration of the rope = Acceleration of the block = 2.4 m/s^2
mass of the rope = 0.480kg
Force = 0.480*2.4 = 1.152 N
and it was wrong. anyone know where i messed up?
 

Answers and Replies

  • #2
Delphi51
Homework Helper
3,407
10
The pull on the rope must accelerate not only the rope but the ice as well.
Add the 1.152 onto the 19.2

Another way to look at it is that the rope has unknown F pulling it forward, and 19.2 N pulling backward. Using sum of forces = ma, this is
ma = F - 19.2
F = ma + 19.2
 
  • #3
rl.bhat
Homework Helper
4,433
5
Force on the rope = Applied force - reaction force by the block.
 
  • #4
oh! i dont know why i didn't catch that. thank you so much!
 

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