2–64.
In a certain machine, the effort
moves 20 feet for every foot that
the resistance moves.
If the
machine is 75 percent efficient,
the force required to overcome a
resistance of 300 pounds is
1.
15 lb
2.
20 lb
3.
25 lb
4.
30 lb
2–65.
If a block and tackle has a
theoretical mechanical advantage of
5 and an efficiency of 60 percent,
the amount of force necessary to
lift a 1,200–pound load is
1.
30 lb
2.
150 lb
3.
400 lb
4.
720 lb
2–66.
Which of the following statements
concerning the relationship of work
output and work input of a machine
is correct?
1.
The output is the same as the
input
2.
The output is greater than the
input
3.
The output is less than the
input
4.
The output has no relationship
to the input
2-67.
The amount of work done divided by
the time required is called
1.
energy
2.
resistance
3.
force
4.
power
When answering questions 2–68
o
through 2–73, assume 100 percent
efficiency in each situation and use the
appropriate power formula to calculate the
unknown quantity.
2–68.
A motor–driven hoist lifts a
165–pound load to a height of 50
feet in 30 seconds.
How much power
does the motor develop?
1.
1/4 hp
2.
1/2 hp
3.
3 hp
4.
10 hp
2–69.
A power winch is capable of lifting
a 440-pound load a distance of 5
feet in 1 second.
The driving
motor works at the rate of
1.
1/2 hp
2.
1 hp
3.
2 hp
4.
4 hp
2–70.
What is the horsepower of the
engine driving the pump that lifts
9,900,000 pounds of water per day
from a lake to the top of a
standpipe,
a vertical distance of
120 feet? The engine runs at a
uniform speed 12 hours a day.
1.
12 hp
2.
15 hp
3.
24 hp
4.
50 hp
2–71.
While a propeller–driven aircraft
travels at a speed of 120 mph, its
engine develops 1,500 hp.
Approximately what force in pounds
is being exerted by the propeller?
1.
850 lb
2.
5,000 lb
3.
15,000 lb
4.
30,000 lb
2–72.
What is the horsepower of a
hoisting engine that can raise
6,000 pounds through a height of 44
feet in one minute?
1.
3 hp
2.
4 hp
3.
8 hp
4.
12 hp
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