Information for items 2–44 through
@
2–46:
YOU are using a first–class
lever to raise a 400–pound load to a
height of 1 foot.
The effort arm of your
lever is 8 feet long and the resistance
arm is 2 feet long.
2–44.
How much work is done in raising
the load?
1.
400 ft–lb
2.
300 ft–lb
3.
200 ft–lb
4.
50 ft–lb
2–45.
How far must you move the lever in
order to raise the load 1 foot?
1.
1 ft
2.
2 ft
3.
8 ft
4.
4 ft
2-46.
How much work is done in balancing
the load at the 1-foot height?
1.
0 ft–lb
2.
2 ft–lb
3.
8 ft–lb
4.
10 ft–lb
2–47.
By using a machine to move an
object you can
1.
decrease the amount of work to
be done
2.
reduce the weight of the object
3.
decrease the amount of the
effort required
4.
reduce the resistance of the
object
Information for questions 2–48
o
through 2–51:
You are using a
24,000–pound load with a screwjack that
has a pitch of 1/4 inch and a 24-inch
handle.
2–48.
Theoretically, (by neglecting
friction),
you should be able to
turn the jack handle by exerting an
effort of about
1.
24 lb
2.
40 lb
3.
60 lb
4.
80 lb
2-49.
Because of friction. you actually
have to apply a 120–pound force to
turn the jack handle.
About how
much work do you do in turning the
handle one complete revolution?
1.
120 ft–lb
2.
240 ft–lb
3.
1,500 ft–lb
4.
3,000 ft–lb
2–50.
With each revolution of the jack
handle, the work output of the jack
equals
1.
100 ft-lb
2.
200 ft-lb
3.
500 ft–lb
4.
600 ft–lb
2–51.
The efficiency of the jack is
1.
12 1/2%
2.
33 1/3%
3.
50
%
4.
66 2/3%
Information for questions 2–52
o
through 2–54:
You push with a
force of 125 pounds to slide a 250–pound
crate up a gangplank.
The gangplank is 12
feet long and the upper end is 5 feet
above
2–52.
2-53.
2-54.
the lower end.
What is the theoretical mechanical
advantage of the gangplank?
1.
1
2.
2
3.
2.4
4.
12
How much of your 125–pound push is
used to overcome friction?
1.
21
lb
2.
42
lb
3.
62 1/2 lb
4.
125
lb
What is the efficiency of the
gangplank?
1.
25%
2.
50%
3.
75%
4.
83.3%
18
