1018
  • 1018
please help with #s 3 and 4. thanks! (problems are in the picture below)
Mathematics
  • Stacey Warren - Expert brainly.com
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SOLVED
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jamiebookeater
  • jamiebookeater
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1018
  • 1018
1 Attachment
welshfella
  • welshfella
Not sure about number 3 but i can help with number 4
welshfella
  • welshfella
|dw:1442848903125:dw|

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welshfella
  • welshfella
let a be acceleration , t tension in the string, coefficient of friction = 0.45 equation of motion of block A_ Newtons 2nd law; T - 0.45*2.25g = 2.25 * a equation of motion of block B:- 1.3g - T = 1.3 * a
welshfella
  • welshfella
solve these 2 equations to find T and a
welshfella
  • welshfella
you can find the speed of the bodies after 3 cm by using one of the equations for constant acceleration
welshfella
  • welshfella
you can use g = 9.81N
1018
  • 1018
i got 2.97 for acceleration
1018
  • 1018
is that correct? i got 2 equations from each block then combined those two equations
welshfella
  • welshfella
i got 0.794 for acceleration
welshfella
  • welshfella
and Tension = 11.72N
1018
  • 1018
can i see your work? thanks
1018
  • 1018
i have a question. in block B, i made the equation Tension - Weight = ma
1018
  • 1018
T=W+ma
welshfella
  • welshfella
T - 9.933 = 2.25a 12.753 - T = 1.3a adding eliminates T 2.82 = 3.55a a = 0.794 ms-2
1018
  • 1018
yes, but shouldnt be tension positive, and weight is negative? or am i wrong with my analysis?
welshfella
  • welshfella
you have to take account of the friction the frictional force = 0.45 * wieght
1018
  • 1018
no, for block B. there's no friction
welshfella
  • welshfella
the tension is positive for 2.25 block and negative for block B
welshfella
  • welshfella
oh sorry block B force = weight - T
1018
  • 1018
im still confused. haha. wait let me draw
1018
  • 1018
|dw:1442851287028:dw|
1018
  • 1018
the direction of the tension is upward right, and weight is downward. so i thought its summation of forces would be T-W=ma
1018
  • 1018
or is this analysis wrong?
welshfella
  • welshfella
the resultant force acts downwards weight acts down tensions acts up
1018
  • 1018
so, tension is positive right, if it acts upward?
welshfella
  • welshfella
No it w - t = ma
welshfella
  • welshfella
don't worry too much about positive or negative the point is that the motion is downwards and there for the net force acts downwards
1018
  • 1018
haha, ok. i'll just try it again. but when i get the acceleration, i can just sub it to one of the equations right? to get tension
welshfella
  • welshfella
yes
1018
  • 1018
and then for speed, just use one of the constant acceleration formulas?
welshfella
  • welshfella
yea m use v^2 = u^2 + 2as
welshfella
  • welshfella
u = iniital velocity = 0
welshfella
  • welshfella
sorry i gotta go right now i think you can finish it OK
1018
  • 1018
thanks!
welshfella
  • welshfella
yw
welshfella
  • welshfella
For number 3 , as the speed is constant I think the force applied will equal the tension in the string. In other words the forces are in equilibrium. what do you think?
1018
  • 1018
wait let me check 3 again
1018
  • 1018
the first thing i did is to make resultant forces = 0 for it is constant speed. is that right?
welshfella
  • welshfella
yes thats what i meant by equilibrium
1018
  • 1018
oh i think i see what you're saying. my solution is not like that. it has frictions
welshfella
  • welshfella
well frictions must play a part
1018
  • 1018
yep but the F is not equal to the tension in my solution
welshfella
  • welshfella
the force must be just enough to overcome the frictions
1018
  • 1018
but the strings on A and B should be equal right? they have the same tension
welshfella
  • welshfella
yes
welshfella
  • welshfella
is the force equal to the sum of the frictional forces on A and B?
welshfella
  • welshfella
that would be 1.8*0.3 + 4.6*0.3?
1018
  • 1018
here's what i did : Block B : Fx = -F + Tension + friction 1 + friction 2 = 0
1018
  • 1018
pretty much yes, but i included tension
welshfella
  • welshfella
yea to be honest i'm not sure of this one.
1018
  • 1018
haha, that's ok i'll try to review with other questions first. haha. thanks though! big help.
welshfella
  • welshfella
yw

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