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Force

Statics · FE Reference Handbook section

Statics
1 formulas
10 exam-style examples
~47 min
All Statics lectures

Handbook notes for this section

Definitions and conditions exactly as the handbook states them.

  • The vector form of a force is

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 — Force

Two forces act at a gusset plate: 44 kN at 22° and 81 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=44kNat22∘F_{1} = 44 kN at 22^{\circ}
  • F2=81kNat139∘F_{2} = 81 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

    44cos22∘=40.80kN,44sin22∘=16.48kN44cos22^{\circ} = 40.80 kN, 44sin22^{\circ} = 16.48 kN
  3. F₂ components

    81cos139∘=−61.13kN,81sin139∘=53.14kN81cos139^{\circ} = -61.13 kN, 81sin139^{\circ} = 53.14 kN
  4. Sums — ΣFₓ = -20.34 kN, ΣF_y = 69.62 kN

  5. Formula — R = √(ΣFₓ² + ΣF_y²)

  6. Substituting

    R=(−20.342+69.622)=72.53kNat106.3∘R = \sqrt(-20.34^{2} + 69.62^{2}) = 72.53 kN at 106.3^{\circ}
Answer:
R=72.53kNactingat106.3∘fromthex−axisR = 72.53 kN acting at 106.3^{\circ} from the x-axis

Why the other options are there

  • 125 kN (magnitudes added)
  • 20.34 kN (y-component dropped)

Reference: FE Reference Handbook — Statics → Force

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

Two forces act at a gusset plate: 69 kN at 20° and 83 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=69kNat20∘F_{1} = 69 kN at 20^{\circ}
  • F2=83kNat130∘F_{2} = 83 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

    69cos20∘=64.84kN,69sin20∘=23.60kN69cos20^{\circ} = 64.84 kN, 69sin20^{\circ} = 23.60 kN
  3. F₂ components

    83cos130∘=−53.35kN,83sin130∘=63.58kN83cos130^{\circ} = -53.35 kN, 83sin130^{\circ} = 63.58 kN
  4. Sums — ΣFₓ = 11.49 kN, ΣF_y = 87.18 kN

  5. Formula — R = √(ΣFₓ² + ΣF_y²)

  6. Substituting

    R=(11.492+87.182)=87.93kNat82.5∘R = \sqrt(11.49^{2} + 87.18^{2}) = 87.93 kN at 82.5^{\circ}
Answer:
R=87.93kNactingat82.5∘fromthex−axisR = 87.93 kN acting at 82.5^{\circ} from the x-axis

Why the other options are there

  • 152 kN (magnitudes added)
  • 11.49 kN (y-component dropped)

Reference: FE Reference Handbook — Statics → Force

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

Two forces act at a gusset plate: 26 kN at 49° and 46 kN at 163° from the positive x-axis. Resolve each force into components and determine the magnitude and direction of the resultant force.

Given

  • F1=26kNat49∘F_{1} = 26 kN at 49^{\circ}
  • F2=46kNat163∘F_{2} = 46 kN at 163^{\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

    26cos49∘=17.06kN,26sin49∘=19.62kN26cos49^{\circ} = 17.06 kN, 26sin49^{\circ} = 19.62 kN
  3. F₂ components

    46cos163∘=−43.99kN,46sin163∘=13.45kN46cos163^{\circ} = -43.99 kN, 46sin163^{\circ} = 13.45 kN
  4. Sums — ΣFₓ = -26.93 kN, ΣF_y = 33.07 kN

  5. Formula — R = √(ΣFₓ² + ΣF_y²)

  6. Substituting

    R=(−26.932+33.072)=42.65kNat129.2∘R = \sqrt(-26.93^{2} + 33.07^{2}) = 42.65 kN at 129.2^{\circ}
Answer:
R=42.65kNactingat129.2∘fromthex−axisR = 42.65 kN acting at 129.2^{\circ} from the x-axis

Why the other options are there

  • 72 kN (magnitudes added)
  • 26.93 kN (y-component dropped)

Reference: FE Reference Handbook — Statics → Force

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

Two forces act at a gusset plate: 47 kN at 53° and 53 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=47kNat53∘F_{1} = 47 kN at 53^{\circ}
  • F2=53kNat120∘F_{2} = 53 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

    47cos53∘=28.29kN,47sin53∘=37.54kN47cos53^{\circ} = 28.29 kN, 47sin53^{\circ} = 37.54 kN
  3. F₂ components

    53cos120∘=−26.50kN,53sin120∘=45.90kN53cos120^{\circ} = -26.50 kN, 53sin120^{\circ} = 45.90 kN
  4. Sums — ΣFₓ = 1.79 kN, ΣF_y = 83.44 kN

  5. Formula — R = √(ΣFₓ² + ΣF_y²)

  6. Substituting

    R=(1.792+83.442)=83.45kNat88.8∘R = \sqrt(1.79^{2} + 83.44^{2}) = 83.45 kN at 88.8^{\circ}
Answer:
R=83.45kNactingat88.8∘fromthex−axisR = 83.45 kN acting at 88.8^{\circ} from the x-axis

Why the other options are there

  • 100 kN (magnitudes added)
  • 1.79 kN (y-component dropped)

Reference: FE Reference Handbook — Statics → Force

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

Two forces act at a gusset plate: 71 kN at 50° and 40 kN at 118° from the positive x-axis. Resolve each force into components and determine the magnitude and direction of the resultant force.

Given

  • F1=71kNat50∘F_{1} = 71 kN at 50^{\circ}
  • F2=40kNat118∘F_{2} = 40 kN at 118^{\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

    71cos50∘=45.64kN,71sin50∘=54.39kN71cos50^{\circ} = 45.64 kN, 71sin50^{\circ} = 54.39 kN
  3. F₂ components

    40cos118∘=−18.78kN,40sin118∘=35.32kN40cos118^{\circ} = -18.78 kN, 40sin118^{\circ} = 35.32 kN
  4. Sums — ΣFₓ = 26.86 kN, ΣF_y = 89.71 kN

  5. Formula — R = √(ΣFₓ² + ΣF_y²)

  6. Substituting

    R=(26.862+89.712)=93.64kNat73.3∘R = \sqrt(26.86^{2} + 89.71^{2}) = 93.64 kN at 73.3^{\circ}
Answer:
R=93.64kNactingat73.3∘fromthex−axisR = 93.64 kN acting at 73.3^{\circ} from the x-axis

Why the other options are there

  • 111 kN (magnitudes added)
  • 26.86 kN (y-component dropped)

Reference: FE Reference Handbook — Statics → Force

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

Two forces act at a gusset plate: 63 kN at 71° and 69 kN at 122° from the positive x-axis. Resolve each force into components and determine the magnitude and direction of the resultant force.

Given

  • F1=63kNat71∘F_{1} = 63 kN at 71^{\circ}
  • F2=69kNat122∘F_{2} = 69 kN at 122^{\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

    63cos71∘=20.51kN,63sin71∘=59.57kN63cos71^{\circ} = 20.51 kN, 63sin71^{\circ} = 59.57 kN
  3. F₂ components

    69cos122∘=−36.56kN,69sin122∘=58.52kN69cos122^{\circ} = -36.56 kN, 69sin122^{\circ} = 58.52 kN
  4. Sums — ΣFₓ = -16.05 kN, ΣF_y = 118.1 kN

  5. Formula — R = √(ΣFₓ² + ΣF_y²)

  6. Substituting

    R=(−16.052+118.12)=119.2kNat97.7∘R = \sqrt(-16.05^{2} + 118.1^{2}) = 119.2 kN at 97.7^{\circ}
Answer:
R=119.2kNactingat97.7∘fromthex−axisR = 119.2 kN acting at 97.7^{\circ} from the x-axis

Why the other options are there

  • 132 kN (magnitudes added)
  • 16.05 kN (y-component dropped)

Reference: FE Reference Handbook — Statics → Force

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

Two forces act at a gusset plate: 71 kN at 20° and 68 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=71kNat20∘F_{1} = 71 kN at 20^{\circ}
  • F2=68kNat141∘F_{2} = 68 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

    71cos20∘=66.72kN,71sin20∘=24.28kN71cos20^{\circ} = 66.72 kN, 71sin20^{\circ} = 24.28 kN
  3. F₂ components

    68cos141∘=−52.85kN,68sin141∘=42.79kN68cos141^{\circ} = -52.85 kN, 68sin141^{\circ} = 42.79 kN
  4. Sums — ΣFₓ = 13.87 kN, ΣF_y = 67.08 kN

  5. Formula — R = √(ΣFₓ² + ΣF_y²)

  6. Substituting

    R=(13.872+67.082)=68.50kNat78.3∘R = \sqrt(13.87^{2} + 67.08^{2}) = 68.50 kN at 78.3^{\circ}
Answer:
R=68.50kNactingat78.3∘fromthex−axisR = 68.50 kN acting at 78.3^{\circ} from the x-axis

Why the other options are there

  • 139 kN (magnitudes added)
  • 13.87 kN (y-component dropped)

Reference: FE Reference Handbook — Statics → Force

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

Two forces act at a gusset plate: 43 kN at 17° and 90 kN at 135° from the positive x-axis. Resolve each force into components and determine the magnitude and direction of the resultant force.

Given

  • F1=43kNat17∘F_{1} = 43 kN at 17^{\circ}
  • F2=90kNat135∘F_{2} = 90 kN at 135^{\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

    43cos17∘=41.12kN,43sin17∘=12.57kN43cos17^{\circ} = 41.12 kN, 43sin17^{\circ} = 12.57 kN
  3. F₂ components

    90cos135∘=−63.64kN,90sin135∘=63.64kN90cos135^{\circ} = -63.64 kN, 90sin135^{\circ} = 63.64 kN
  4. Sums — ΣFₓ = -22.52 kN, ΣF_y = 76.21 kN

  5. Formula — R = √(ΣFₓ² + ΣF_y²)

  6. Substituting

    R=(−22.522+76.212)=79.47kNat106.5∘R = \sqrt(-22.52^{2} + 76.21^{2}) = 79.47 kN at 106.5^{\circ}
Answer:
R=79.47kNactingat106.5∘fromthex−axisR = 79.47 kN acting at 106.5^{\circ} from the x-axis

Why the other options are there

  • 133 kN (magnitudes added)
  • 22.52 kN (y-component dropped)

Reference: FE Reference Handbook — Statics → Force

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

Two forces act at a gusset plate: 43 kN at 64° and 83 kN at 123° from the positive x-axis. Resolve each force into components and determine the magnitude and direction of the resultant force.

Given

  • F1=43kNat64∘F_{1} = 43 kN at 64^{\circ}
  • F2=83kNat123∘F_{2} = 83 kN at 123^{\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

    43cos64∘=18.85kN,43sin64∘=38.65kN43cos64^{\circ} = 18.85 kN, 43sin64^{\circ} = 38.65 kN
  3. F₂ components

    83cos123∘=−45.21kN,83sin123∘=69.61kN83cos123^{\circ} = -45.21 kN, 83sin123^{\circ} = 69.61 kN
  4. Sums — ΣFₓ = -26.36 kN, ΣF_y = 108.3 kN

  5. Formula — R = √(ΣFₓ² + ΣF_y²)

  6. Substituting

    R=(−26.362+108.32)=111.4kNat103.7∘R = \sqrt(-26.36^{2} + 108.3^{2}) = 111.4 kN at 103.7^{\circ}
Answer:
R=111.4kNactingat103.7∘fromthex−axisR = 111.4 kN acting at 103.7^{\circ} from the x-axis

Why the other options are there

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

Reference: FE Reference Handbook — Statics → Force

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

Two forces act at a gusset plate: 20 kN at 70° and 21 kN at 135° from the positive x-axis. Resolve each force into components and determine the magnitude and direction of the resultant force.

Given

  • F1=20kNat70∘F_{1} = 20 kN at 70^{\circ}
  • F2=21kNat135∘F_{2} = 21 kN at 135^{\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

    20cos70∘=6.84kN,20sin70∘=18.79kN20cos70^{\circ} = 6.84 kN, 20sin70^{\circ} = 18.79 kN
  3. F₂ components

    21cos135∘=−14.85kN,21sin135∘=14.85kN21cos135^{\circ} = -14.85 kN, 21sin135^{\circ} = 14.85 kN
  4. Sums — ΣFₓ = -8.01 kN, ΣF_y = 33.64 kN

  5. Formula — R = √(ΣFₓ² + ΣF_y²)

  6. Substituting

    R=(−8.012+33.642)=34.58kNat103.4∘R = \sqrt(-8.01^{2} + 33.64^{2}) = 34.58 kN at 103.4^{\circ}
Answer:
R=34.58kNactingat103.4∘fromthex−axisR = 34.58 kN acting at 103.4^{\circ} from the x-axis

Why the other options are there

  • 41 kN (magnitudes added)
  • 8.01 kN (y-component dropped)

Reference: FE Reference Handbook — Statics → Force

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