Name:__________________________
Period (class #/letter)_______
Machines and Efficiency
Date:____________
[35 points (with 2 bonus pts for date and on time)]
Answer all the questions. Show all your work and
units!!!
Actual Mechanical Advantage=Force out/Force in
Ideal Mechanical Advantage=Distance in/Distance out
1. A crate of bananas weighing 3000 N is shipped from South America to New York, where it is unloaded by a dock
worker who lifts the crate by pulling with a force of 200 N on the rope of a pulley system. What is the actual
mechanical advantage of the pulley system? (2 pts)
Actual Mechanical Advantage=Force out/Force in
Fout=
Fin=200N
Actual Mechanical Advantage =______________
2. You and your sibling are fooling around in the summer and decide to make a seesaw. Your younger sibling, with
a mass of 50 kg, stand at the lower end of the seesaw while you, with
a mass of 80 kg, jumps on the raised side of the seesaw, propelling
your sibling into the air. (FYI: do not try this at home!!!) (5 pts)
a. What is the idea mechanical advantage of the seesaw?? (2 pts)
Ideal Mechanical Advantage=Distance in/Distance out
din=2.40 m
dout=
Ideal Mechanical Advantage =______________
b. If you exert a force of 850 N on the seesaw when you jump, how much force is exerted on your smaller
sibling? (3 pts).
Fout=?
Fin=850 N
din=2.40 m
dout=
Force out=______________
Name:__________________________
Period (class #/letter)_______
Date:____________
3. A jackscrew with a handle 30.0 cm (r) long is used to lift a car sitting on the jack. The car rises 2.0 cm for every
full turn of the handle (2πr). What is the ideal mechanical advantage of the jack?. (4 pts)
a. What is the idea mechanical advantage of the seesaw?? (2 pts)
Ideal Mechanical Advantage=Distance in/Distance out
din=2πr=
dout=height it rises=
Ideal Mechanical Advantage =______________
4. It is Halloween, and you want to scare the innocent kids as they come to your house to get candy. You decide
that a flying ghost will do the trick, so you rig up a harness on a pulley. Your friend weighs about 150 lbs (682 N)
and is hoisted into the tree. If it takes 88 N of force to keep the ghost “floating” by the pulley, what is the actual
mechanical advantage? (2 pts)
Actual Mechanical Advantage=Force out/Force in
Fout=
Fin=
Actual Mechanical Advantage =______________
5. A windmill uses sails blown by the wind to turn an axle that allows a millstone to grind corn into
meal with a force of 90N. The windmill has sails of radius 6.0 m blown by a wind that exerts a
force of 15N on the sails, and the axle of the grindstone has a radius of 0.50 m.
( 6 pts)
a. What is the idea mechanical advantage of the wheel?? (2 pts)
Ideal Mechanical Advantage=Distance in/Distance out (hint:
din=rin=6.0 M
dout=
; 2π crosses out)
Ideal Mechanical Advantage =______________
b. What is the actual mechanical advantage of the wheel? (2 pts)
Actual Mechanical Advantage=Force out/Force in
Fout=
Fin=
Actual Mechanical Advantage =______________
c.
What is the efficiency of the wheel? (2 pts).
Efficiency=______________
Name:__________________________
Period (class #/letter)_______
Date:____________
6. You get a job as a waiter/waitress, and are required to serve with a tray in
one hand. The tray weighs 5.0 N, and you place 12 dishes, each weighing
3.5 N. Your arm is 30.0 cm form your elbow to your hand, and your biceps
muscle exerts a force of 5.0cm on the elbow, which acts as a fulcrum. How
much force must her biceps exert to allow you to hold the tray? (3 pts)
Look at “d”, that is 5.0 cm!!!
Fout=
Fbicep=?
din=
dout=
Force bicep=______________
7. A Wheel Horse “A-90 Lawn Tractor” weighs about 600 lbs (2727N). You are helping power equipment with the
tractor deliver after it gets a tune-up. You have a ramp on the back of your truck which is 6.0 meters long and
1.0 m off the ground to your bed. ( 6 pts)
a. What is the idea mechanical advantage of the incline?? (2 pts)
Ideal Mechanical Advantage =______________
b. If it takes 600 N to push the tractor up the ramp at a constant speed, what is the actual mechanical
advantage of the incline? (2 pts)
Actual Mechanical Advantage =______________
c.
What is the efficiency of the wheel? (2 pts).
Efficiency=______________
Name:__________________________
Period (class #/letter)_______
Date:____________
8. Mr. Reymond uses a screwdriver with a handle of radius 1.2 cm to remove a screw in the
back of a computer. The screw moves out 0.20 cm on each complete turn. What is the
ideal mechanical advantage of the screwdriver? (2 pts) (HINT: din=2πr, and r is given!!!)
Ideal Mechanical Advantage =______________
9. Your buddy loves to fish, so you decide to go. (7 pts)
a. How much work (input) is required for your buddy to reel in a 10.0 kg bluefish from the water’s surface
to the deck of a fishing boat, 5.20 m above the water, if the reel of his fishing pole is 85% efficient?
(HINT: Get force first, and remember what work is!!!) (3 pts).
Total Work =______________
b. If your buddy applies a force of 15 N to the reel’s crank handle, what is the actual mechanical advantage
of the fishing pole? (2 pts)
Actual Mechanical Advantage =______________
c. What is the ideal mechanical advantage of the fishing pole? (2 pts)
Ideal Mechanical Advantage =______________
10. KE/PE/Work Review: Wile E. Coyote, whose mass is 20.0
kg, is chasing the roadrunner when the coyote
accidentally runs off the edge of a cliff and plummets to
the ground 30.0 m below. What force does the ground
exert on the coyote as he makes a coyote-shaped dent
0.420 m deep in the ground? (3 pts)
Force =______________