Download Chapter 7 1. An elevator consists of a motor and pulley system to lift

Chapter 7
1. An elevator consists of a motor and pulley system to lift the carriage up
and down. If the work into the system is 2000ftLb and the system performs
1500ftLb of work, what is the efficiency of the system?
2. A car jack delivers 1200Lb of force to a bumper of a car. A force of 10Lb
is delivered to the jack handle. What is the mechanical advantage of the
jack?
3. Inside a copy machine is a compound machine consisting of a screw with
a mechanical advantage of 1200 and a pulley system with a mechanical
advantage of 4. What is the total mechanical advantage?
4. An automated soldering station consists of a soldering iron that is
translated back and forth on a threaded shaft. The pitch of the threads is
0.05in and at the end of the shaft is a handle of radius 1.0in and is driven by
a motor. If it takes 1.5Lbs of force to translate the iron back and forth, how
much force does the motor deliver to the shaft? Assume an efficiency of 0.9.
5. A knob on an oscilloscope has a diameter of 1.5in and is connected to a
shaft of 0.25in. If the knob is turned with 1.1Lbs of force, what force is the
shaft turned with if the efficiency equals 1?
6. A vending machine dispenses some candy by pushing the candy up an
inclined plane of length 9in and a height 3in. The candy then falls down a
shoot to be removed. If the candy weighs 0.15Lb, how much force is the
candy pushed with? Assume an efficiency of 0.8.
7. A robotic arm raises a 25N weight. The weight is 50cm form the elbow
joint and a cable is connected 20cm from the joint and is used to raise and
lower the arm. How much force is needed to raise the weight? Assume the
efficiency is 1.
8. The efficiency of a log-splitting wedge is very low. Assume it is 0.2. The
wedge is 12in long and 1in wide and a hammer strikes the wedge with a
force of 100Lb. What force is delivered to the log?
9. A robot contains a compound machine consisting of three basic machines
with mechanical advantages of 4, 5, and 6. If the drive system to the
machines can generate a force of 10Lb, what weight can the robot lift?
10. If a compound machine consists of two machines, one with an efficiency
of 0.9 and the other an efficiency of 0.8, what is the total efficiency?
11. What is the MA of a machine if with 10Lb of input force the machine
can lift 120Lb?
12. A machine has 100ftLb of work put into it but only performs 80ftLb of
work. What is the percent efficiency of the machine?
13. A machine not well lubricated will have a low efficiency because of
friction. If the efficiency of the machine is only 0.4 and 20Nm of work is put
into the machine, what is the output of the machine?
14. The handle of a car jack moves through a distance of 2.5ft and the car
moves up 0.005ft with each pump of the jack handle. If the efficiency of the
jack is 0.6, what is the MA?
15. A read/write head on a hard drive is mounted on a lever. The head is
mounted 10cm from a pivot, the actuator of the lever arm is mounted 2cm
form the pivot. Assume 100% efficiency, what is the MA of this lever?
16. A pulley system mounted inside a robotic arm consists of 4 strands. The
applied force to the last strand moves in the same direction as the load put on
the arm. If the input force to the pulleys is 20Lbs, how much can the arm
lift? (Assume an efficiency of 0.75)
17. A compound machine consists of two basic machines with efficiencies
of 0.9 and 0.8. What is the total efficiency of this compound machine?
18. A steering wheel on a car of diameter 50cm is connected to a shaft 1cm.
If 12N of force is applied to the wheel what force is output to the 1cm shaft?
(Assume an efficiency of 1)
59. A ¼-20 screw is used to level the legs on a table. The table weighs
100Lb so each leg supports 25Lb. If the screws are turned with a wrench that
is 6in long, how much force is needed to raise the table? (Assume an
efficiency of 0.75)
20. A compound machine consists of 3 simple machines with MA’s of 12,
14, and 50. What is the total MA of this machine?