Demo: Drawing of FBD and obtaining reactions (with force pair)

Draw the corresponding free body diagram.

Use paired arrows of the same color to show forces that are equal and opposite due to Newton's 3rd Law. When using paired vectors, try to draw two-force members in tension.

Grading info: paired vectors are graded in the pairs that they were formed. All combinations are checked, but the pair is graded all-or-nothing. The colors cycle, but that's just a visual aid (delete any vector to also remove its paired vector, and get a fresh color).

(The expected tolerance is 1/2 square grid for position and 10 degrees for angle.)



Correct answer

Student view placeholder

In student views this area is used for assessment and score info.
Tools

Staff information

Question

Title:
Demo: Drawing of FBD and obtaining reactions (with force pair)

Variant

Started at:
2026-08-04 22:42:33 (CDT)
Duration:
0s
Show/Hide answer
{
  "box": [
    {
      "id": 0,
      "x1": 80,
      "x2": 200,
      "x3": 340,
      "y1": 280,
      "y2": 100,
      "y3": 100,
      "type": "pl-3pointrod",
      "color": "#ffffff",
      "graded": false,
      "height": 20,
      "label1": "A",
      "label2": "B",
      "label3": "C",
      "stroke": "#000000",
      "drawPin": true,
      "evented": false,
      "offsetx1": 20,
      "offsetx2": 0,
      "offsetx3": 0,
      "offsety1": -20,
      "offsety2": 10,
      "offsety3": 10,
      "selectable": false,
      "gradingName": "pl-3pointrod",
      "strokeWidth": 2
    },
    {
      "id": 1,
      "top": 100,
      "fill": "#000000",
      "left": 340,
      "type": "pl-arc-dimensions",
      "angle": 0,
      "label": "\\\\theta",
      "graded": false,
      "radius": 60,
      "stroke": "#000000",
      "evented": false,
      "offsetx": 10,
      "offsety": 0,
      "originY": "center",
      "endAngle": 0,
      "selectable": false,
      "startAngle": -50,
      "gradingName": "pl-arc-dimensions",
      "strokeWidth": 1,
      "drawEndArrow": true,
      "drawStartArrow": true,
      "endSupportLine": true,
      "drawCenterPoint": false,
      "startSupportLine": true,
      "arrowheadWidthRatio": 1,
      "arrowheadOffsetRatio": 1
    },
    {
      "id": 2,
      "top": 280,
      "fill": "#808080",
      "left": 340,
      "type": "pl-circle",
      "label": "",
      "graded": false,
      "radius": 60,
      "stroke": "#000000",
      "evented": false,
      "offsetx": 5,
      "offsety": 5,
      "opacity": 1,
      "originX": "center",
      "originY": "center",
      "scaling": true,
      "selectable": false,
      "gradingName": "pl-circle",
      "strokeWidth": 1,
      "strokeUniform": true
    },
    {
      "id": 3,
      "top": 280,
      "fill": "#000000",
      "left": 340,
      "type": "pl-point",
      "label": "C",
      "graded": false,
      "radius": 4,
      "evented": false,
      "offsetx": 5,
      "offsety": 5,
      "opacity": 1,
      "originX": "center",
      "originY": "center",
      "selectable": false,
      "gradingName": "pl-point",
      "widthErrorBox": 20,
      "heightErrorBox": 20,
      "XcenterErrorBox": 340,
      "YcenterErrorBox": 280,
      "objectDrawErrorBox": null
    },
    {
      "id": 4,
      "top": 318.56725658119234,
      "fill": "#000000",
      "left": 385.9626665871387,
      "type": "pl-point",
      "label": "",
      "graded": false,
      "radius": 4,
      "evented": false,
      "offsetx": 5,
      "offsety": 5,
      "opacity": 1,
      "originX": "center",
      "originY": "center",
      "selectable": false,
      "gradingName": "pl-point",
      "widthErrorBox": 20,
      "heightErrorBox": 20,
      "XcenterErrorBox": 385.9626665871387,
      "YcenterErrorBox": 318.56725658119234,
      "objectDrawErrorBox": null
    },
    {
      "id": 5,
      "x1": 200,
      "y1": 100,
      "top": 40,
      "left": 200,
      "type": "pl-vector",
      "angle": 90,
      "label": "",
      "width": 60,
      "graded": true,
      "stroke": "#c72c1c",
      "evented": false,
      "offsetx": 2,
      "offsety": 2,
      "originY": "center",
      "selectable": false,
      "gradingName": "pl-vector",
      "strokeWidth": 3,
      "trueHandles": [
        "mtr"
      ],
      "drawEndArrow": true,
      "drawErrorBox": true,
      "widthErrorBox": 80,
      "drawStartArrow": false,
      "heightErrorBox": 20,
      "offset_forward": 0,
      "XcenterErrorBox": 200,
      "YcenterErrorBox": 70,
      "disregard_sense": false,
      "offset_backward": 60,
      "optional_grading": false,
      "objectDrawErrorBox": null,
      "arrowheadWidthRatio": 1,
      "arrowheadOffsetRatio": 1
    },
    {
      "id": 6,
      "x1": 80,
      "y1": 280,
      "top": 280,
      "left": 80,
      "type": "pl-vector",
      "angle": 0,
      "label": "",
      "width": 60,
      "graded": true,
      "stroke": "#c72c1c",
      "evented": false,
      "offsetx": 2,
      "offsety": 2,
      "originY": "center",
      "selectable": false,
      "gradingName": "pl-vector",
      "strokeWidth": 3,
      "trueHandles": [
        "mtr"
      ],
      "drawEndArrow": true,
      "drawErrorBox": true,
      "widthErrorBox": 140,
      "drawStartArrow": false,
      "heightErrorBox": 20,
      "offset_forward": 60,
      "XcenterErrorBox": 80,
      "YcenterErrorBox": 280,
      "disregard_sense": true,
      "offset_backward": 60,
      "optional_grading": false,
      "objectDrawErrorBox": null,
      "arrowheadWidthRatio": 1,
      "arrowheadOffsetRatio": 1
    },
    {
      "id": 7,
      "x1": 80,
      "y1": 280,
      "top": 280,
      "left": 80,
      "type": "pl-vector",
      "angle": -90,
      "label": "",
      "width": 60,
      "graded": true,
      "stroke": "#c72c1c",
      "evented": false,
      "offsetx": 2,
      "offsety": 2,
      "originY": "center",
      "selectable": false,
      "gradingName": "pl-vector",
      "strokeWidth": 3,
      "trueHandles": [
        "mtr"
      ],
      "drawEndArrow": true,
      "drawErrorBox": true,
      "widthErrorBox": 140,
      "drawStartArrow": false,
      "heightErrorBox": 20,
      "offset_forward": 60,
      "XcenterErrorBox": 80,
      "YcenterErrorBox": 280,
      "disregard_sense": true,
      "offset_backward": 60,
      "optional_grading": false,
      "objectDrawErrorBox": null,
      "arrowheadWidthRatio": 1,
      "arrowheadOffsetRatio": 1
    },
    {
      "id": 8,
      "x1": 385.9626665871387,
      "y1": 318.56725658119234,
      "top": 357.1345131623847,
      "left": 431.9253331742774,
      "type": "pl-vector",
      "angle": -140,
      "label": "",
      "width": 60,
      "graded": true,
      "stroke": "#c72c1c",
      "evented": false,
      "offsetx": 2,
      "offsety": 2,
      "originY": "center",
      "selectable": false,
      "gradingName": "pl-vector",
      "strokeWidth": 3,
      "trueHandles": [
        "mtr"
      ],
      "drawEndArrow": true,
      "drawErrorBox": true,
      "widthErrorBox": 140,
      "drawStartArrow": false,
      "heightErrorBox": 20,
      "offset_forward": 60,
      "XcenterErrorBox": 385.9626665871387,
      "YcenterErrorBox": 318.56725658119234,
      "disregard_sense": true,
      "offset_backward": 60,
      "optional_grading": false,
      "objectDrawErrorBox": null,
      "arrowheadWidthRatio": 1,
      "arrowheadOffsetRatio": 1
    },
    {
      "id": 9,
      "x1": 340,
      "x2": 340,
      "y1": 100,
      "y2": 280,
      "top1": 100,
      "top2": 280,
      "type": "pl-paired-vector",
      "label": "",
      "left1": 340,
      "left2": 340,
      "width": 60,
      "angle1": -140,
      "angle2": 40,
      "graded": true,
      "stroke": "#c72c1c",
      "evented": false,
      "offsetx": 2,
      "offsety": 2,
      "originY": "center",
      "selectable": false,
      "gradingName": "pl-paired-vector",
      "strokeWidth": 3,
      "trueHandles": [
        "mtr"
      ],
      "drawEndArrow": true,
      "drawErrorBox": true,
      "drawStartArrow": false,
      "offset_forward": 60,
      "widthErrorBox1": 140,
      "widthErrorBox2": 140,
      "disregard_sense": true,
      "heightErrorBox1": 20,
      "heightErrorBox2": 20,
      "offset_backward": 60,
      "XcenterErrorBox1": 340,
      "XcenterErrorBox2": 340,
      "YcenterErrorBox1": 100,
      "YcenterErrorBox2": 280,
      "optional_grading": false,
      "objectDrawErrorBox": null,
      "arrowheadWidthRatio": 1,
      "arrowheadOffsetRatio": 1
    }
  ]
}
History
dec frac
rad deg