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Resolution of a Force

Statics · FE Reference Handbook section

Statics
4 formulas
10 exam-style examples
~53 min
All Statics lectures

Core formulas for this FE topic

Definitions, applicability, units, assumptions and worked examples for each relation.

Worked exam-style examples

The four ways this section is written on the real exam — thoughts first, then equations, then substitution.

Example 1
Resolution of a force system into a single resultant — Resolution of a Force

Two forces act at a gusset plate: 20 kN at 43° and 65 kN at 130° from the positive x-axis. Resolve each force into components and determine the magnitude and direction of the resultant force.

Given

  • F1=20kNat43∘F_{1} = 20 kN at 43^{\circ}
  • F2=65kNat130∘F_{2} = 65 kN at 130^{\circ}

Find

Resultant force magnitude R and its direction

Start with the thinking

  • A force system is resolved by summing x- and y-components separately.
  • The resultant of concurrent forces is the vector sum, never the arithmetic sum of magnitudes.

Step-by-step solution

  1. Formula

    Fx=Fcos⁡θ,Fy=Fsin⁡θFₓ = F \cos \theta, F_y = F \sin \theta
  2. F₁ components

    20cos43∘=14.63kN,20sin43∘=13.64kN20cos43^{\circ} = 14.63 kN, 20sin43^{\circ} = 13.64 kN
  3. F₂ components

    65cos130∘=−41.78kN,65sin130∘=49.79kN65cos130^{\circ} = -41.78 kN, 65sin130^{\circ} = 49.79 kN
  4. Sums — ΣFₓ = -27.15 kN, ΣF_y = 63.43 kN

  5. Formula — R = √(ΣFₓ² + ΣF_y²)

  6. Substituting

    R=(−27.152+63.432)=69.00kNat113.2∘R = \sqrt(-27.15^{2} + 63.43^{2}) = 69.00 kN at 113.2^{\circ}
Answer:
R=69.00kNactingat113.2∘fromthex−axisR = 69.00 kN acting at 113.2^{\circ} from the x-axis

Why the other options are there

  • 85 kN (magnitudes added)
  • 27.15 kN (y-component dropped)

Reference: FE Reference Handbook — Statics → Resolution of a Force

Example 2
Resolution of a force system into a single resultant — Resolution of a Force (2)

Two forces act at a gusset plate: 36 kN at 20° and 90 kN at 139° from the positive x-axis. Resolve each force into components and determine the magnitude and direction of the resultant force.

Given

  • F1=36kNat20∘F_{1} = 36 kN at 20^{\circ}
  • F2=90kNat139∘F_{2} = 90 kN at 139^{\circ}

Find

Resultant force magnitude R and its direction

Start with the thinking

  • A force system is resolved by summing x- and y-components separately.
  • The resultant of concurrent forces is the vector sum, never the arithmetic sum of magnitudes.

Step-by-step solution

  1. Formula

    Fx=Fcos⁡θ,Fy=Fsin⁡θFₓ = F \cos \theta, F_y = F \sin \theta
  2. F₁ components

    36cos20∘=33.83kN,36sin20∘=12.31kN36cos20^{\circ} = 33.83 kN, 36sin20^{\circ} = 12.31 kN
  3. F₂ components

    90cos139∘=−67.92kN,90sin139∘=59.05kN90cos139^{\circ} = -67.92 kN, 90sin139^{\circ} = 59.05 kN
  4. Sums — ΣFₓ = -34.09 kN, ΣF_y = 71.36 kN

  5. Formula — R = √(ΣFₓ² + ΣF_y²)

  6. Substituting

    R=(−34.092+71.362)=79.08kNat115.5∘R = \sqrt(-34.09^{2} + 71.36^{2}) = 79.08 kN at 115.5^{\circ}
Answer:
R=79.08kNactingat115.5∘fromthex−axisR = 79.08 kN acting at 115.5^{\circ} from the x-axis

Why the other options are there

  • 126 kN (magnitudes added)
  • 34.09 kN (y-component dropped)

Reference: FE Reference Handbook — Statics → Resolution of a Force

Example 3
Resolution of a force system into a single resultant — Resolution of a Force (3)

Two forces act at a gusset plate: 80 kN at 37° and 58 kN at 126° from the positive x-axis. Resolve each force into components and determine the magnitude and direction of the resultant force.

Given

  • F1=80kNat37∘F_{1} = 80 kN at 37^{\circ}
  • F2=58kNat126∘F_{2} = 58 kN at 126^{\circ}

Find

Resultant force magnitude R and its direction

Start with the thinking

  • A force system is resolved by summing x- and y-components separately.
  • The resultant of concurrent forces is the vector sum, never the arithmetic sum of magnitudes.

Step-by-step solution

  1. Formula

    Fx=Fcos⁡θ,Fy=Fsin⁡θFₓ = F \cos \theta, F_y = F \sin \theta
  2. F₁ components

    80cos37∘=63.89kN,80sin37∘=48.15kN80cos37^{\circ} = 63.89 kN, 80sin37^{\circ} = 48.15 kN
  3. F₂ components

    58cos126∘=−34.09kN,58sin126∘=46.92kN58cos126^{\circ} = -34.09 kN, 58sin126^{\circ} = 46.92 kN
  4. Sums — ΣFₓ = 29.80 kN, ΣF_y = 95.07 kN

  5. Formula — R = √(ΣFₓ² + ΣF_y²)

  6. Substituting

    R=(29.802+95.072)=99.63kNat72.6∘R = \sqrt(29.80^{2} + 95.07^{2}) = 99.63 kN at 72.6^{\circ}
Answer:
R=99.63kNactingat72.6∘fromthex−axisR = 99.63 kN acting at 72.6^{\circ} from the x-axis

Why the other options are there

  • 138 kN (magnitudes added)
  • 29.80 kN (y-component dropped)

Reference: FE Reference Handbook — Statics → Resolution of a Force

Example 4
Resolution of a force system into a single resultant — Resolution of a Force (4)

Two forces act at a gusset plate: 31 kN at 34° and 68 kN at 120° from the positive x-axis. Resolve each force into components and determine the magnitude and direction of the resultant force.

Given

  • F1=31kNat34∘F_{1} = 31 kN at 34^{\circ}
  • F2=68kNat120∘F_{2} = 68 kN at 120^{\circ}

Find

Resultant force magnitude R and its direction

Start with the thinking

  • A force system is resolved by summing x- and y-components separately.
  • The resultant of concurrent forces is the vector sum, never the arithmetic sum of magnitudes.

Step-by-step solution

  1. Formula

    Fx=Fcos⁡θ,Fy=Fsin⁡θFₓ = F \cos \theta, F_y = F \sin \theta
  2. F₁ components

    31cos34∘=25.70kN,31sin34∘=17.33kN31cos34^{\circ} = 25.70 kN, 31sin34^{\circ} = 17.33 kN
  3. F₂ components

    68cos120∘=−34.00kN,68sin120∘=58.89kN68cos120^{\circ} = -34.00 kN, 68sin120^{\circ} = 58.89 kN
  4. Sums — ΣFₓ = -8.30 kN, ΣF_y = 76.22 kN

  5. Formula — R = √(ΣFₓ² + ΣF_y²)

  6. Substituting

    R=(−8.302+76.222)=76.68kNat96.2∘R = \sqrt(-8.30^{2} + 76.22^{2}) = 76.68 kN at 96.2^{\circ}
Answer:
R=76.68kNactingat96.2∘fromthex−axisR = 76.68 kN acting at 96.2^{\circ} from the x-axis

Why the other options are there

  • 99 kN (magnitudes added)
  • 8.30 kN (y-component dropped)

Reference: FE Reference Handbook — Statics → Resolution of a Force

Example 5
Resolution of a force system into a single resultant — Resolution of a Force (5)

Two forces act at a gusset plate: 64 kN at 45° and 48 kN at 147° from the positive x-axis. Resolve each force into components and determine the magnitude and direction of the resultant force.

Given

  • F1=64kNat45∘F_{1} = 64 kN at 45^{\circ}
  • F2=48kNat147∘F_{2} = 48 kN at 147^{\circ}

Find

Resultant force magnitude R and its direction

Start with the thinking

  • A force system is resolved by summing x- and y-components separately.
  • The resultant of concurrent forces is the vector sum, never the arithmetic sum of magnitudes.

Step-by-step solution

  1. Formula

    Fx=Fcos⁡θ,Fy=Fsin⁡θFₓ = F \cos \theta, F_y = F \sin \theta
  2. F₁ components

    64cos45∘=45.25kN,64sin45∘=45.25kN64cos45^{\circ} = 45.25 kN, 64sin45^{\circ} = 45.25 kN
  3. F₂ components

    48cos147∘=−40.26kN,48sin147∘=26.14kN48cos147^{\circ} = -40.26 kN, 48sin147^{\circ} = 26.14 kN
  4. Sums — ΣFₓ = 5.00 kN, ΣF_y = 71.40 kN

  5. Formula — R = √(ΣFₓ² + ΣF_y²)

  6. Substituting

    R=(5.002+71.402)=71.57kNat86.0∘R = \sqrt(5.00^{2} + 71.40^{2}) = 71.57 kN at 86.0^{\circ}
Answer:
R=71.57kNactingat86.0∘fromthex−axisR = 71.57 kN acting at 86.0^{\circ} from the x-axis

Why the other options are there

  • 112 kN (magnitudes added)
  • 5.00 kN (y-component dropped)

Reference: FE Reference Handbook — Statics → Resolution of a Force

Example 6
Resolution of a force system into a single resultant — Resolution of a Force (6)

Two forces act at a gusset plate: 87 kN at 57° and 74 kN at 143° from the positive x-axis. Resolve each force into components and determine the magnitude and direction of the resultant force.

Given

  • F1=87kNat57∘F_{1} = 87 kN at 57^{\circ}
  • F2=74kNat143∘F_{2} = 74 kN at 143^{\circ}

Find

Resultant force magnitude R and its direction

Start with the thinking

  • A force system is resolved by summing x- and y-components separately.
  • The resultant of concurrent forces is the vector sum, never the arithmetic sum of magnitudes.

Step-by-step solution

  1. Formula

    Fx=Fcos⁡θ,Fy=Fsin⁡θFₓ = F \cos \theta, F_y = F \sin \theta
  2. F₁ components

    87cos57∘=47.38kN,87sin57∘=72.96kN87cos57^{\circ} = 47.38 kN, 87sin57^{\circ} = 72.96 kN
  3. F₂ components

    74cos143∘=−59.10kN,74sin143∘=44.53kN74cos143^{\circ} = -59.10 kN, 74sin143^{\circ} = 44.53 kN
  4. Sums — ΣFₓ = -11.72 kN, ΣF_y = 117.5 kN

  5. Formula — R = √(ΣFₓ² + ΣF_y²)

  6. Substituting

    R=(−11.722+117.52)=118.1kNat95.7∘R = \sqrt(-11.72^{2} + 117.5^{2}) = 118.1 kN at 95.7^{\circ}
Answer:
R=118.1kNactingat95.7∘fromthex−axisR = 118.1 kN acting at 95.7^{\circ} from the x-axis

Why the other options are there

  • 161 kN (magnitudes added)
  • 11.72 kN (y-component dropped)

Reference: FE Reference Handbook — Statics → Resolution of a Force

Example 7
Resolution of a force system into a single resultant — Resolution of a Force (7)

Two forces act at a gusset plate: 68 kN at 62° and 33 kN at 141° from the positive x-axis. Resolve each force into components and determine the magnitude and direction of the resultant force.

Given

  • F1=68kNat62∘F_{1} = 68 kN at 62^{\circ}
  • F2=33kNat141∘F_{2} = 33 kN at 141^{\circ}

Find

Resultant force magnitude R and its direction

Start with the thinking

  • A force system is resolved by summing x- and y-components separately.
  • The resultant of concurrent forces is the vector sum, never the arithmetic sum of magnitudes.

Step-by-step solution

  1. Formula

    Fx=Fcos⁡θ,Fy=Fsin⁡θFₓ = F \cos \theta, F_y = F \sin \theta
  2. F₁ components

    68cos62∘=31.92kN,68sin62∘=60.04kN68cos62^{\circ} = 31.92 kN, 68sin62^{\circ} = 60.04 kN
  3. F₂ components

    33cos141∘=−25.65kN,33sin141∘=20.77kN33cos141^{\circ} = -25.65 kN, 33sin141^{\circ} = 20.77 kN
  4. Sums — ΣFₓ = 6.28 kN, ΣF_y = 80.81 kN

  5. Formula — R = √(ΣFₓ² + ΣF_y²)

  6. Substituting

    R=(6.282+80.812)=81.05kNat85.6∘R = \sqrt(6.28^{2} + 80.81^{2}) = 81.05 kN at 85.6^{\circ}
Answer:
R=81.05kNactingat85.6∘fromthex−axisR = 81.05 kN acting at 85.6^{\circ} from the x-axis

Why the other options are there

  • 101 kN (magnitudes added)
  • 6.28 kN (y-component dropped)

Reference: FE Reference Handbook — Statics → Resolution of a Force

Example 8
Resolution of a force system into a single resultant — Resolution of a Force (8)

Two forces act at a gusset plate: 58 kN at 48° and 80 kN at 127° from the positive x-axis. Resolve each force into components and determine the magnitude and direction of the resultant force.

Given

  • F1=58kNat48∘F_{1} = 58 kN at 48^{\circ}
  • F2=80kNat127∘F_{2} = 80 kN at 127^{\circ}

Find

Resultant force magnitude R and its direction

Start with the thinking

  • A force system is resolved by summing x- and y-components separately.
  • The resultant of concurrent forces is the vector sum, never the arithmetic sum of magnitudes.

Step-by-step solution

  1. Formula

    Fx=Fcos⁡θ,Fy=Fsin⁡θFₓ = F \cos \theta, F_y = F \sin \theta
  2. F₁ components

    58cos48∘=38.81kN,58sin48∘=43.10kN58cos48^{\circ} = 38.81 kN, 58sin48^{\circ} = 43.10 kN
  3. F₂ components

    80cos127∘=−48.15kN,80sin127∘=63.89kN80cos127^{\circ} = -48.15 kN, 80sin127^{\circ} = 63.89 kN
  4. Sums — ΣFₓ = -9.34 kN, ΣF_y = 107.0 kN

  5. Formula — R = √(ΣFₓ² + ΣF_y²)

  6. Substituting

    R=(−9.342+107.02)=107.4kNat95.0∘R = \sqrt(-9.34^{2} + 107.0^{2}) = 107.4 kN at 95.0^{\circ}
Answer:
R=107.4kNactingat95.0∘fromthex−axisR = 107.4 kN acting at 95.0^{\circ} from the x-axis

Why the other options are there

  • 138 kN (magnitudes added)
  • 9.34 kN (y-component dropped)

Reference: FE Reference Handbook — Statics → Resolution of a Force

Example 9
Resolution of a force system into a single resultant — Resolution of a Force (9)

Two forces act at a gusset plate: 68 kN at 22° and 33 kN at 165° from the positive x-axis. Resolve each force into components and determine the magnitude and direction of the resultant force.

Given

  • F1=68kNat22∘F_{1} = 68 kN at 22^{\circ}
  • F2=33kNat165∘F_{2} = 33 kN at 165^{\circ}

Find

Resultant force magnitude R and its direction

Start with the thinking

  • A force system is resolved by summing x- and y-components separately.
  • The resultant of concurrent forces is the vector sum, never the arithmetic sum of magnitudes.

Step-by-step solution

  1. Formula

    Fx=Fcos⁡θ,Fy=Fsin⁡θFₓ = F \cos \theta, F_y = F \sin \theta
  2. F₁ components

    68cos22∘=63.05kN,68sin22∘=25.47kN68cos22^{\circ} = 63.05 kN, 68sin22^{\circ} = 25.47 kN
  3. F₂ components

    33cos165∘=−31.88kN,33sin165∘=8.54kN33cos165^{\circ} = -31.88 kN, 33sin165^{\circ} = 8.54 kN
  4. Sums — ΣFₓ = 31.17 kN, ΣF_y = 34.01 kN

  5. Formula — R = √(ΣFₓ² + ΣF_y²)

  6. Substituting

    R=(31.172+34.012)=46.14kNat47.5∘R = \sqrt(31.17^{2} + 34.01^{2}) = 46.14 kN at 47.5^{\circ}
Answer:
R=46.14kNactingat47.5∘fromthex−axisR = 46.14 kN acting at 47.5^{\circ} from the x-axis

Why the other options are there

  • 101 kN (magnitudes added)
  • 31.17 kN (y-component dropped)

Reference: FE Reference Handbook — Statics → Resolution of a Force

Example 10
Resolution of a force system into a single resultant — Resolution of a Force (10)

Two forces act at a gusset plate: 83 kN at 50° and 89 kN at 154° from the positive x-axis. Resolve each force into components and determine the magnitude and direction of the resultant force.

Given

  • F1=83kNat50∘F_{1} = 83 kN at 50^{\circ}
  • F2=89kNat154∘F_{2} = 89 kN at 154^{\circ}

Find

Resultant force magnitude R and its direction

Start with the thinking

  • A force system is resolved by summing x- and y-components separately.
  • The resultant of concurrent forces is the vector sum, never the arithmetic sum of magnitudes.

Step-by-step solution

  1. Formula

    Fx=Fcos⁡θ,Fy=Fsin⁡θFₓ = F \cos \theta, F_y = F \sin \theta
  2. F₁ components

    83cos50∘=53.35kN,83sin50∘=63.58kN83cos50^{\circ} = 53.35 kN, 83sin50^{\circ} = 63.58 kN
  3. F₂ components

    89cos154∘=−79.99kN,89sin154∘=39.02kN89cos154^{\circ} = -79.99 kN, 89sin154^{\circ} = 39.02 kN
  4. Sums — ΣFₓ = -26.64 kN, ΣF_y = 102.6 kN

  5. Formula — R = √(ΣFₓ² + ΣF_y²)

  6. Substituting

    R=(−26.642+102.62)=106.0kNat104.6∘R = \sqrt(-26.64^{2} + 102.6^{2}) = 106.0 kN at 104.6^{\circ}
Answer:
R=106.0kNactingat104.6∘fromthex−axisR = 106.0 kN acting at 104.6^{\circ} from the x-axis

Why the other options are there

  • 172 kN (magnitudes added)
  • 26.64 kN (y-component dropped)

Reference: FE Reference Handbook — Statics → Resolution of a Force

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