Engineering Mechanics ENGG*1210,Winter2013
MidtermReview
Assigned: Tuesday, February ,
-. e connected bar BC is used to increase the lever arm of the crescent wrench as shown.
If a clockwise moment of A = N ▯ m is needed to tighten the nut at A and the extension
is d = mm, determine the required force F in order to develop this moment.
Midterm Review
-. e chain AB exerts a force of lb on the door at B. Determine the magnitude of the
moment of this force along the hinged axis x of the door. Midterm Review
-. A boy stands out at the end of the diving board, which is supported by two springs A and
B, each having a stiﬀness of k = kN/m. In the position shown, the board is horizontal.
If the boy has a mass of kg, determine the angle of tilt which the board makes with the
horizontal aer he jumps oﬀ. Neglect the weight of the board and assume it is rigid. Midterm Review
-. Due to an unequal distribution of fuel in the wing tanks, the centres of gravity for the
airplane fuselage A and wings B and C are located as shown. If these components have
weights W = lb, W = lb, and W = lb, determine the normal reactions of
A B C
the wheels D, E, and F on the ground. 4–29.
The connected bar BC is used to increase the lever arm of C
the cre scent wrench a s shown. If a clockwi se moment of
M A = 120 N m is needed to ti ghten the nut at A and the
extension d = 300 mm, determine the required forF in
d 15⬚ F
order to develop this moment.
30⬚
300 mm
B
SOLUTION
A
By resolving force F into components parallel and perpendicular to the box wrench
BC,Fi g. a, the moment of F can be obtained by addin g algebraically the moments
of the se two component s about poinA in accordance with the principle of
moments.
a +(M R A =© Fd; -120 = Fsin15°(0.3sin30°) - Fcos15°(0.3cos30° + 0.3)
F = 239 N Ans. 4–50.
The chain AB exerts a force of 20 lb on the door at B. z
Determine the magnitude of the moment of this force along
the hinged axis x of the door.
3ft
2ft
A
F =20lb
SOLUTION O B
y
Position Vector and Force Vector: 4ft
r

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