# ENGI 1313 Mechanics I - Memorial University of Newfoundland

ENGI 1313 Mechanics I Lecture 42: Course Material Review Shawn Kenny, Ph.D., P.Eng. Assistant Professor Faculty of Engineering and Applied Science Memorial University of Newfoundland [email protected] Example 42-01 2 If the resultant couple moment of the three couples acting on the triangular block is to be zero, determine the magnitudes of forces F and P. 2007 S. Kenny, Ph.D., P.Eng. ENGI 1313 Statics I Lecture 42

Example 42-01 (cont.) Technical Concept Couple Moment M R Fd M R r F 3 2007 S. Kenny, Ph.D., P.Eng. ENGI 1313 Statics I Lecture 42 Example 42-01 (cont.) Analysis M 0 y

3 F 6 in 10 lb 2 2 3 4 3 in 0 d d d F 3 lb M z 0 4 P 6 in 10 lb

32 42 3 in 0 P 4 lb 4 2007 S. Kenny, Ph.D., P.Eng. ENGI 1313 Statics I Lecture 42 Example 42-02 5 The telephone pole of negligible thickness is subjected to the force of 80 lb directed as shown. It is supported by the cable BCD and can be assumed pinned at its base A. In order to provide clearance for a sidewalk right of way, where D is located, the strut CE is attached at C, as shown by the dashed lines

(cable segment CD is removed). If the tension in CD is to be twice the tension in BCD, determine the height h for placement of the strut CE. 2007 S. Kenny, Ph.D., P.Eng. ENGI 1313 Statics I Lecture 42 Example 42-02 (cont.) Technical Approach 2D Equilibrium FBD Complete FBD? TBD Yes for initial condition Find TBD Ax Ay 6

2007 S. Kenny, Ph.D., P.Eng. ENGI 1313 Statics I Lecture 42 Example 42-02 (cont.) Find TBD M 0 TBD A 80 lb cos 30 30 ft 10 TBD 2 2 30 10 30 ft 0 TBD 219.1lb

Ax Ay 7 2007 S. Kenny, Ph.D., P.Eng. ENGI 1313 Statics I Lecture 42 Example 42-02 (cont.) Find TCD TCD' 2TBD 2 219.1lb 438.2 lb TBD Find LCE M 0 A 80 lb cos 30 30 ft TCD' LCE 0 LCE 4.74 ft Find h

30 ft 30 ft h 10 ft 4.74 ft 8 TCD Ax Ay h 15.8 ft 2007 S. Kenny, Ph.D., P.Eng. ENGI 1313 Statics I Lecture 42 Example 42-03 9 The pipe is hoisted using the tongs. If the coefficient of static friction at A and B is s, determine the smallest dimension b so that any pipe of inner diameter d can be lifted. 2007 S. Kenny, Ph.D., P.Eng.

ENGI 1313 Statics I Lecture 42 Example 42-03 (cont.) W Global FBD F 0 y W 2 FB 0.5W FBD of Tong M 0 C d b N

h F 0 B B 2 W 2b d NB 4h FB W 2 10 2007 S. Kenny, Ph.D., P.Eng. Cx NB Cy FB ENGI 1313 Statics I Lecture 42

FB Example 42-03 (cont.) W For Lifting W 2 FB W 2b d NB 4h 0.5W FB s NB W s W 2 b d 2 4h FB 2 h s 2 b d h d b

s 2 11 2007 S. Kenny, Ph.D., P.Eng. Cx NB Cy FB ENGI 1313 Statics I Lecture 42 FB References Hibbeler (2007) http://wps.prenhall.com/ esm_hibbeler_engmech_1 12 2007 S. Kenny, Ph.D., P.Eng. ENGI 1313 Statics I Lecture 42

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