Conceptual
What are Newton's Three Laws?
1. An object in motion must remain in motion and an object at rest must remain at rest unless acted on by an outside force.
2. F = ma
3. Every action has an equal and opposite re-action.
Draw the force diagram of an object in free fall.
I can't insert pictures so pretend this is just a single arrow labeled Fg on a box or point. Bonus points for adding air resistance arrow (not really)
What force replaces the normal force in a hanging mass question?
The tension of the rope
In 99.99% of all situations (according to Dr. Evans), what is true about coefficients of friction?
μs > μk
What does it mean for an object to be in free fall?
The onyl force acting on it is gravity, Fg.
Draw the force diagram of two people pushing on a 50kg box. One person pushes to the left with a force of 200N and the other person pushes with a force of 350N.
No pictures :/ there should be four arrows on your box
If you can accelerate a mass of 50kg with a force of 300N, then what is the magnitude of the acceleration?
F = ma
F/m = a
300N/50kg = a
a = 6 m/s2
A table with μs = 0.88 has a book that weighs 20kg. How much force must be applied to get the object moving?
μsN = fs,max
Fg = N = mg = 20kg * 9.8m/s2 = 196N
0.88 * 196N = 172.48N
If you push on a box with force Fpush and it doesn't move, what can we assume about the frictional force?
fs = Fpush
A 10kg teletubby hangs from a string, probably because Dr. Evans put it there. Draw the force diagram if I were to push on the teletubby from the left with a force of 50N.
There should be three arrows: Fg, T (NOT normal force), and Fpush.
If I hang a 10kg rock from the ceiling, and an 8kg rock from the first rock, what is the tension in the rope connecting the first rock to the ceiling? Assume the string is massless.
8kg + 10kg = 18kg
Fg = may = mg = 18kg * 9.8m/s2 = 176.4N
Why does the normal force change when you pull upward on an object, even if it doesn't actually move at all?
Since the object isn't moving, we know Fnet,y = 0N. So N - mg = 0 → N = mg. However, pulling upward means adding another force to the equation. But the object isn't moving so the net force is still zero. N + F = mg. Therefore, N has to be smaller in order to balance the equation.
When a car tire rolls without slipping, what form of friction does it have? (Between static and kinetic friction)
Static friction. Kinetic friction happens when the wheel is slipping or locked up.
A textbook with mass m sits on a tilted table, at an angle θ above the horizontal. Assuming the book isn't sliding, draw the force diagram for this scenario. Break all vectors into components as needed.
Taking the tilted surface as the new "coordinate plane", there should be N pointing upward, f pointing up the ramp, mgsinθ pointing down the ramp, and mgcosθ pointing into the ramp (opposing N)
A three year old ties all eight of his identical toy cars together and pulls the first one on a string with a force of 100N, how much tension is in each of the strings?
100N, 87.5N, 75N, 62.5N, 50N, 37.5N, 25N, 12.5N
If gravitational acceleration is the same for everything then why do things have different gravitational forces?
Look at F = ma. If acceleration stays constant, then the only two variables changing are F and m. If F increases, then m must increase as well to match. So something heavier is pulled harder downward so it accelerates at the same as something light.
If the third law of motion says that every force has an equal and opposite reaction, then how does anything ever move at all?
The forces act on OPPOSITE objects so they don't cancel each other out.
Draw the force diagram for a worker pulling a 200kg box on a rope at 45° above the horizontal with a rope tension of 410N that does not move. Solve for approx. values for all forces.
Normal and mg as they should be. Break pulling force into components with Fcosθ being the horizontal and Fsinθ being the vertical that makes the normal smaller. Remember mg = N + Fsinθ. Friction force is equal to Fcosθ in opposite direction.
I'm applying a force F to a mass m at an acceleration a. Then my friend comes over and applies a force 3F. What happens to the acceleration?
The acceleration quadruples.
F + 3F = 4F
4F = m*4a
A box is held up by a rope connected to a metal ring, which has two identical ropes holding it up from the ceiling. What is the angle between the two ropes if the tension in the single string is 1.60 times the tension in one of the ropes above the ring? (See drawing)
74°
(It's too much to type out here so I’ll write it on the board)