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Forces review
Not much space, guess you’ll have to be succinct. 
1. Define acceleration.
2. Define velocity.
3. How is velocity different from speed?
4. Define a force.
5. When forces on an object total zero, what happens if the object is already still? what happens if
something’s already moving?
6. When forces on an object do not total zero what happens?
7. What is Newton’s 1st Law?
8. What is Newton’s 2nd Law?
9. What is Newton’s 3rd Law?
10. What is Newton’s 4th Law?
11. What is Fg and which direction does it point?
12. What is Fa?
13. What is Fn and which direction does it point?
14. What is Ff, Fs, Fk, and Fsmax and what direction do they all point?
15. Define μk.
16. Define μs.
17. What is an action/reaction pair? Give an example.
18. When do you use a = 9.81m/s2?
19. Does your notecard have any of the above info you were not sure about?
20. Does your notecard have the steps to solving a force problem written on it?
21. Does your notecard have the three friction coefficient equations on it?
22. Each person complete one step at a time for the following problem. A 2kg soccer ball is falling
straight down after a fierce headbutt straight up. As the ball is falling, the wind blows with a force of 8N
to the right. Calculate the final force and the acceleration of the soccer ball.
a. Draw a dot to represent a 2kg soccer ball falling through the air.
b. Draw a vector to represent Fg. (no numbers)
c. Calculate Fg.
d. Draw a vector to represent Fa for the wind, including the magnitude of the force.
e. Draw the vector that will represent the final force on the soccer ball.
f. Calculate the magnitude of the final force on the soccer ball. (Remember, vectors can slide)
g. Calculate the acceleration of the soccer ball. (Remember, acceleration is a vector. That means
there is a magnitude and a direction)
23. Each person complete one step at a time for the following problem. A 3000kg car is being gently pushed
by a well-trained rhinoceros to the left with a force of 12000N. At the same time, the flashy animal
trainer is pulling the car to the left with a rope using a force of 120N at 12° above the ground. μk
between the ground and the car is 0.4. Find the car’s acceleration.
a. Draw a dot to represent a 3000kg car sitting on the ground.
b. Add vectors (no numbers) to represent Fg and Fn.
c. Add a vector to represent the rhinoceros gently pushing the car with a 12000N force to the left,
parallel to the ground.
d. Add a vector to represent the animal trainer pulling the car with a rope to the left with a force of
120N at a 12° angle to the ground.
e. Add a vector (no number) to represent Fk.
f. Calculate Fax and Fay.
g. Calculate Fg.
h. Calculate Fn.
i. Calculate Fk if the coefficient of friction between the floor and the car is 0.4.
j. Calculate ƩFx
k. Calculate the acceleration of the car. (Remember, acceleration is a vector. That means there is a
magnitude and a direction)
24. If the situation in #23 were on a 15° slope, what additional steps would you do to solve the problem?
25. If it takes 325N of force to start a picnic table sliding across the ground, is this equivalent to Fs, Fsmax,
or Fk?
26. If the picnic table’s mass is 400kg, what is its weight?
27. If it takes 310N of force to keep the picnic table moving once it’s started, what is the value of Fk?
28. What is the μs between the picnic table and the ground?
29. What is the μk between the picnic table and the ground?
Forces review key
Not much space, guess you’ll have to be succinct. 
1. Define acceleration. Change in speed or direction
2. Define velocity. Speed in a given direction
3. How is velocity different from speed? Direction
4. Define a force. Push or a pull
5. When forces on an object total zero, what happens if the object is already still? what happens if
something’s already moving? No change
6. When forces on an object do not total zero what happens? Change
7. What is Newton’s 1st Law? Object at rest…unbalanced force. Aka law of inertia
8. What is Newton’s 2nd Law? F=ma
9. What is Newton’s 3rd Law? Action/reaction; equal and opposite reaction
10. What is Newton’s 4th Law? There’s not one
11. What is Fg and which direction does it point? Force due to gravity, always down
12. What is Fa? Applied force
13. What is Fn and which direction does it point? Natural/normal force; perpendicular to the surface
14. What is Ff, Fs, Fk, and Fsmax and what direction do they all point? Force of friction/static
friction/kinetic friction/maximum static friction; all opposite ƩF
15. Define μk. Coefficient of kinetic friction; how ‘sticky’ two surfaces are during motion
16. Define μs. Coefficient of static friction; how ‘sticky’ two surfaces are during force but before motion
17. What is an action/reaction pair? Give an example. I push on the wall; wall pushes back w/= force
18. When do you use a = 9.81m/s2? Fg
19. Does your notecard have any of the above info you were not sure about?
20. Does your notecard have the steps to solving a force problem written on it?
21. Does your notecard have the three friction coefficient equations on it?
22. Each person complete one step at a time for the following problem. A 2kg soccer ball is falling
straight down after a fierce headbutt straight up. As the ball is falling, the wind blows with a force of 8N
to the right. Calculate the final force and the acceleration of the soccer ball.
a. Draw a dot to represent a 2kg soccer ball falling through the air.
b. Draw a vector to represent Fg. (no numbers)
c. Calculate Fg. F=ma=2(9.81)=19.62N
d. Draw a vector to represent Fa for the wind, including the magnitude of the force.
e. Draw the vector that will represent the final force on the soccer ball.
f. Calculate the magnitude of the final force on the soccer ball. (Remember, vectors can slide)
g. Calculate the acceleration of the soccer ball. (Remember, acceleration is a vector. That means
there is a magnitude and a direction)
19.62 + 82 = c2
21.2 = c
θ = tan-1 (8/19.6) = 22° right of down
Fa 8N
F = ma
21.2 = 2a
a = 10.6 m/s2
Fg 19.6N
Fg 19.6N
Fa 8N
23. Each person complete one step at a time for the following problem. A 3000kg car is being gently pushed
by a well-trained rhinoceros to the left with a force of 12000N. At the same time, the flashy animal
trainer is pulling the car to the left with a rope using a force of 120N at 12° above the ground. μk
between the ground and the car is 0.4. Find the car’s acceleration.
a. Draw a dot to represent a 3000kg car sitting on the ground.
b. Add vectors (no numbers) to represent Fg and Fn.
c. Add a vector to represent the rhinoceros gently pushing the car with a 12000N force to the left,
parallel to the ground.
d. Add a vector to represent the animal trainer pulling the car with a rope to the left with a force of
120N at a 12° angle to the ground.
e. Add a vector (no number) to represent Fk.
f. Calculate Fax and Fay. Faty = sin12(120) = 25N
Fatx = cos12(120) = 117N
g. Calculate Fg. F=ma=3000(9.81) = 29,430N
h. Calculate Fn. Fn = Fg – Faty = 29,430 – 25 = 29,405N
i. Calculate Ff if the coefficient of friction between the floor and the car is 0.4.
μ = Ff/Fn
so
Ff = μ(Fn) = 0.4(29,405) = 11,762N
j. Calculate ƩFx. ƩFx = Far + Fatx – Ff = 12,000 + 117 – 11,762 = 355N
k. Calculate the acceleration of the car. (Remember, acceleration is a vector. That means there is a
magnitude and a direction) F = ma 355 = 3000a a=0.12m/s2 left
Fat 120N
Fn 29,405N
θ=12°
Far 12,000N
Ff 11,762N
Fg 29,430N
24. If the situation in #23 were on a 15° slope, what additional steps would you do to solve the problem?
Tilt x-y by 15°. Find Fgx and Fgy. Fn = Fgy – Faty. Add Fgx to friction to find ƩFx.
25. If it takes 325N of force to start a picnic table sliding across the ground, is this equivalent to Fs, Fsmax,
or Fk? Fsmax
26. If the picnic table’s mass is 400kg, what is its weight? Weight = force = ma = 400(9.81) = 3924N
27. If it takes 310N of force to keep the picnic table moving once it’s started, what is the value of Fk? 310N
28. What is the μs between the picnic table and the ground?
(Fn = Fg b/c flat ground) μs = Fsmax/Fn = 325/3924 = 0.083
29. What is the μk between the picnic table and the ground?
(Fn = Fg b/c flat ground) μk = Fk/Fn = 310/3924 = 0.079