# Mechanics again

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• Oct 9th 2009, 05:25 AM
ramzel
Mechanics again
S1 and S2 are light inextensible strings, and A and B are particles each of mass 0.2 kg. Particles suspended from a fixed point 0 by the string S1 and particle B is suspended from A by the string. The particle hang in equlibirum...

Find tension in s1 and s2

http://img24.imageshack.us/img24/7585/maths2n.png

s1 = 4 N and s2 = 2N

Second part, string S1 is cut and the particles fall, the air resistance acting on A is 0.4N and the air resistance on B is 0.2N

Find acceleration force acting on the particles and tenstion in s2 ???!!

Could someone explain me the concept of this.... exams are close and i dont understand this question at all :(
• Oct 10th 2009, 10:10 AM
skeeter
Quote:

Originally Posted by ramzel
S1 and S2 are light inextensible strings, and A and B are particles each of mass 0.2 kg. Particles suspended from a fixed point 0 by the string S1 and particle B is suspended from A by the string. The particle hang in equlibirum...

Find tension in s1 and s2

http://img24.imageshack.us/img24/7585/maths2n.png

s1 = 4 N and s2 = 2N

Second part, string S1 is cut and the particles fall, the air resistance acting on A is 0.4N and the air resistance on B is 0.2N

Find acceleration force acting on the particles and tenstion in s2 ???!!

Could someone explain me the concept of this.... exams are close and i dont understand this question at all :(

forces acting on mass A ...

$R_A = 0.4$ N up , $T$ down, $mg$ down

$F_{net} = ma$

$T + mg - R_A = ma$

forces acting on mass B ...

$R_B = 0.2$ N up , $T$ up , $mg$ down

$mg - T - R_B = ma$

combine the two equations ...

$2mg - R_A - R_B = 2ma$

$a = \frac{2mg - R_A - R_B}{2m}$

sub in your values to find $a$ , then go back to either equation and calculate $T$.