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A particle of mass 2 kg is connected to another particle of mass 3 kg by a taut light inelastic string which passes over a smooth light pulley at the edge of a rough horizontal table - Leaving Cert Applied Maths - Question 4 - 2013

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A particle of mass 2 kg is connected to another particle of mass 3 kg by a taut light inelastic string which passes over a smooth light pulley at the edge of a rough... show full transcript

Worked Solution & Example Answer:A particle of mass 2 kg is connected to another particle of mass 3 kg by a taut light inelastic string which passes over a smooth light pulley at the edge of a rough horizontal table - Leaving Cert Applied Maths - Question 4 - 2013

Step 1

Show on separate diagrams the forces acting on each particle.

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Answer

For the 2 kg mass on the table:

  • Weight, W1=2gW_1 = 2g
  • Normal force, RR
  • Frictional force, f=12Rf = \frac{1}{2} R
  • Tension, TT in the string.

For the 3 kg mass hanging:

  • Weight, W2=3gW_2 = 3g
  • Tension, TT in the string.

Step 2

Find the common acceleration of the particles.

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Answer

Using Newton’s second law for the 3 kg mass:

  1. 3gT=3a3g - T = 3a

For the 2 kg mass:

  1. T12R2g=2aT - \frac{1}{2} R - 2g = 2a

Since R=2gfR = 2g - f and f=12Rf = \frac{1}{2}R, substituting gives:

  1. T+14R=2aT + \frac{1}{4}R = 2a

Combining and solving these equations leads to:

  1. a=2g5=4m/s2a = \frac{2g}{5} = 4 \, m/s^2.

Step 3

Find the tension in the string.

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Answer

Substituting the acceleration back into the equations gives:

Using T=3g3aT = 3g - 3a leads to:

  1. T=3(10)3(4)=18NT = 3(10) - 3(4) = 18 \, N.

Step 4

Find the common acceleration of the particles.

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Answer

For the 6 kg mass:

  1. 6gcos(30)T=6a6g \cos(30^{\circ}) - T = 6a

For the 2 kg mass:

  1. T2g=2aT - 2g = 2a

Substituting and simplifying gives:

  1. g=8g = 8 leads to a=108=1.25m/s2a = \frac{10}{8} = 1.25 \, m/s^2.

Step 5

Find the tension in the string.

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Answer

Using the calculated acceleration in:

  1. T=2g+2aT = 2g + 2a results in:

  2. T=22.5NT = 22.5 \, N.

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