assignment3 solution - Assignment 3 ES230 Key solutions...

Assignment 3 ES230
Key solutions
Problem 3.1
A 90-N force is applied to the control rod AB as shown. Knowing that the
length of the rod is 225 mm, determine the moment of the force about
point B by resolving the force into components along AB and in a
direction perpendicular to AB .

Problem 3.5
A 2.9-lb force P is applied to the lever which controls the auger of a
snowblower. Determine the value of
α
knowing that the moment of P
about A is counterclockwise and has a magnitude of 17
lb in. ⋅
Solution 5.
By definition
/
sin
A B A
M r P θ =
where
( 29
90 θ φ α = + ° -
and
1
4.8 in.
tan
3.4 in.
φ
-
 
=
 
 
54.689 = °
Also
( 29 ( 29 2 2
/
3.4 in. 4.8 in.
B A
r = +
5.8822 in. =
Then
( 29 ( 29 ( 29 ( 29
17 lb in. 5.8822 in. 2.9 lb sin 54.689 90 α ⋅ = ° + ° -
or
( 29
sin 144.689 0.99658 α ° - =
or
144.689 85.260 ; 94.740 α ° - = ° °
49.9 , 59.4 α ∴ = ° ° t

Problem 3.10
It is known that a force with a moment of
7840 lb in. ⋅
about D is required
to straighten the fence post CD . If 8 a = in., 35 b = in., and
112 d =
in., determine the tension that must be developed in the cable of
winch puller AB to create the required moment about point D .

Problem 3.23