Work and Mechanical Advantage
Name __________________
Period ______________
The formula for work is:
Work (J) = Force (N) x Distance (m)
Joules is the unit for Work
Newton is the unit for Force
Meter is the unit for Distance
1. Amanda lifts a crate into the back of her truck. She exerts a force of 200 N a distance of 1.2 m.
Calculate the amount of work done on the crate.
2. Amanda then uses an inclined plane to push the same crate into the truck. She exerts a force of 80 N
a distance of 3.0 m. What is the work done on the crate?
3.
Which of the above situations did more work, one or two?
4. Which of the above situations used more force, one or two?
5. Which of the above situations used increased distance, one or two?
6. Why did the inclined plane make the force needed less?
7. What 2 factors were changed then the inclined plane was used?
a.
b.
b.b.
88 8. Name the class of lever from the diagram on the left.
8.
Lable
9 9. Label the LOAD, FULCRUM, and EFFORT Force.
1010. Calculate the work done by the arm. (Load has a weight of 75
N and is lifted .32 m.)
The formula for Mechanical Advantage
Mechanical Advantage (MA) =
When using FORCE:
Output (load/resistance) force /Input (effort) force
(MACHINE (machine side)/ME (person side))
When using LENGTH:
Length of Effort (input) Arm/Length Resistance (output/load) Arm
(ME (person side)/MACHINE (machine side))
In this example, Susan and Jake’s truck gets stuck in the mud. They use a tree branch
as a lever to lift the truck out of the mud. They apply 700 N of force to the branch.
The back of the truck weighs 2100N. The mechanical advantage can be calculated by
Output force/Input force
2100/700=3 so the Mechanical Advantage is 3. That
means the Susan and Jake only had to apply 1/3 of the force needed to lift the truck
because they used a lever.
1. Blake and Jordan get stuck in the mud. They apply an effort force of 700N to a log they are using as
a lever. The car weighs 900N. What is the MA?
2. Marc is asked to raise the flag at school. If the effort force to raise the flag is 50N and the load force
(the weight of the flag and the rope) is 50N, what is the mechanical advantage of the pully?
3. Justin is riding his bike up Dunmore Hill. The effort force from his feet on the pedals is 1160N.
The resulting load force to move the bike forward is 675N. What is the mechanical advantage of the
bike?
4. Compare the mechanical advantage from questions 1, 2, and 3. Which situation had the greatest
mechanical advantage?
5.
Which situation had to apply the most force?
6. Which situation would cause you to sweat the least?
A construction worker uses a board and log as a lever to lift a heavy rock. If the
input arm is 3 meters long and the output arm is 0.75 meters long, what is the
mechanical advantage of the lever?
MA___3_____ = Length of effort (input) arm____
.75
Length of resistance (output) arm
The Mechanical advantage of this lever is 4.
7. If the input was 100 N, what was the output force? Hint …
MA=Output force
Input force
8. If a lever had a force arm of 3.2m long and a load arm of .6m long, what is the MA?
9. If Blake and Jordan made the force are .2m instead of 3.2, then
a. What is the MA?
b. Is this easier or harder to lift the load?
10. Examine the diagram below and label the lettered parts. What class is it?
11. What is the MA of the lever above? Show your work. (I want to see the math)
Sometimes levers are used to multiply distance. For a broom, your upper hand
is the fulcrum and your lower hand provides the input force: Notice the input
arm is shorter than the output arm.
12. Label the input arm and the output arm.
The mechanical advantage of this broom is:
MA = 0.3 meter = 0.25
1.2 meters
13. What class lever is this broom?
A mechanical advantage less than one does not mean a machine isn’t useful. It just means that
instead of multiplying force, the machine multiplies distance. A broom doesn’t push the dust with
as much force as you use to push the broom, but a small movement of your arm pushes the dust
a large distance.
14. A lever used to lift a heavy box has an effort arm of 4 meters and a resistance arm of 0.8
meters. What is the mechanical advantage of the lever?
15. What is the mechanical advantage of a lever that has an effort arm of 3 meters and a
resistance arm of 2 meters?
16. A lever with an effort arm of 2 meters has a mechanical advantage of 4. What is the
resistance arm’s length?
17. A lever with a resistance arm of 0.8 meter has a mechanical advantage of 6. What is the
length of the effort arm?
18. A rake is held so that its effort arm is 0.4 meters and its resistance arm is 1.0 meters. What
is the mechanical advantage of the rake?
19. A broom with an effort arm length of 0.4 meters has a mechanical advantage of 0.5. What
is the length of the resistance arm?
20. A child’s toy rake is held so that its resistance arm is 0.75 meters. If the mechanical
advantage is 0.33, what is the effort arm length?
21. A crow bar (lever) is often used to lift a large object. If the crowbar is 100 cm long and the object is
20 cm from the fulcrum, what is the mechanical advantage of the crowbar?
CHEAT SHEET:
If using the LENGTHS of the arms, the formula is:
Effort (input) Arm/Resistance Arm (output)
ME (person side)/MACHINE (machine side)
If using the FORCE (newtons) then the formula is:
Output (resistance)/Input (effort)
ME (person side)/MACHINE (machine side)