26 Chapter 2 • Statics Example 2.4
Determine; (a) (b)
65 N the magnitude of force P, and
the direction of the resultant Q from the information given in fig. 2.3.
Fig. 2.3Fig. 2.3 110°
Method • Select a suitable scale. • Draw the vector of the 65 N force (OA). • Extend a light line fromO in the direction of P. • Extend a dotted line fromA parallel to P. • Determine the length of the resultant fromthe scale. • Draw an arc with a radius equal to the resultant and the centre on O (the point of application of the forces) until it intersects the dotted line.
Q = 79,5 N P
• Draw a line fromO to this intersect (this is the resultant). • Draw a dotted line fromthe intersect, parallel to the 65 N vector until it touches the line extended in the direction of P. Tis is the end of the vector of force P.
• Measure the length of vector P and calculate itsmagnitude. • Measure the angle of the resultant.
Solution:
Scale: 100mm= 79,5 N 100mm 100 = 79 5
100 ,
\1mm= 0,795 N 0,795 N = 1mm
0 795
,N 0,795 = 1mm
0,795 \1 N = 1,258mm OB = 92mm(bymeasurement)
According to the scale: 1mm= 0,795 N 92mm= 92 × 0,795 N
\92mm= 73,14 N = Force P
Angle AOC = 60° C (bymeasurement). (a)
Force P = 73,14 N (b) Resultant pulls 60° below the left horizontal For 65 N force 1 N = 1,258mm = 65 × 1,258mm \65 N = 81,77mm
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