8/13/2019 ES 11 - 1st long exam.doc

1/2

ES 11 FIRST EXAM July 15, 2009

Name: _________________________________________ Student Number: _____________ Section:_____________

Part I. Write the letter corresponding to the best answer on the space provided before the number.

1. Force Ris perpendicular to the !" plane# while force Pis parallel to the $!" plane. If the$ are concurrent# what is trueabout their sum%

a. It is directed towards the positive !ais.b. It is parallel to the !" plane.c. It has no !component.

d. It has non!"ero # $# and " components.

&. 'he following procedures can be used to determine the resultant of several force vectors acting on a particle ()*(P'a. +dding the magnitudes and angles.b. Successive application of the triangle rule.c. Summation of the rectangular components of the forces.d. +dding algebraicall$ the force vectors.

,. -efer to Figure 1./ + ball is suspended b$ , cables tied to a ring. Which is false%a. 'he magnitude of the tensions in each cable is the same.b. 'he sum of the magnitudes of the cable tensions is e0ual to the magnitude of the weight.c. If the ball is lower# the tension in each cable is lesser.d. 'he cable tensions and the weight are concurrent forces.

. Which of the following is true%a. + force ma$ be moved an$where along its line of action without producing a change in eternal effectsb. + force s$stem that is in e0uilibrium can be added to# or removed from another force s$stem without

changing the eternal effect of the latter.c. 'he simplest force s$stem that is e0uivalent to a given force s$stem is called the resultant of the force

s$stem.d. +ll of the above.

2. + weight is suspended b$ three ropes. If the ropes have the same direction cosines# what could be said about thes$stem%

a. It can be in e0uilibrium3 the three ropes have e0ual tensions.b. It can never be in e0uilibriumc. It can be in e0uilibrium3 onl$ two ropes have e0ual tensions.d. It can be in e0uilibrium3 no two ropes have e0ual tensions.

4. 'he force 2N5 is acting at pt. -1#1#1/ # determine the moment about ais 15.a. 162b. 7c. 2d. !2

8. 9arignons 'heorem states thata. 'he moment of the resultant of two concurrent forces about an$ ais perpendicular to the plane of the forces

is e0ual to the algebraic sum of the moments of the two forces about the same ais.b. 'he moment of the resultant of two concurrent forces about an$ ais parallel to the plane of the forces is

e0ual to the algebraic sum of the moments of the two forces about the same ais.c. 'he moment of the resultant of two concurrent forces about an$ ais parallel to the plane of the forces is

e0ual to the vector sum of the moments of the two forces about the same ais.d. None of the above.

;. Provided that point + is in e0uilibrium# the value of F+ and Fiven that the resultant of a force is e0ual to ?-17N/i@ -8&7N/j@ -!,47N/k# Aetermine the direction cosine withrespect to the "!ais.

a. !7.&1;b. 7.&1;c. 17&.4B

d. !17&.4B

17. 'he unit vector along +* is e0ual toa. ?7.448i@ 7.,;1j@ 7.448kb. ?7.84&i@ 7.,;1j! 7.2&kc. ?7.448i@ 7.,;1j! 7.448kd. ?7.84&i@ 7.,;1j@ 7.2&k

Figure 1

47.&4B

47 N

7 N

&7.24B

FB

FA

Figure &

* -14#17#11/

+ -,&8/

8/13/2019 ES 11 - 1st long exam.doc

2/2