AP Physics 1

The three most fundamental equations of this unit (and possibly the whole course) 

• v = v₀ + at

• Δx = v₀t + (1/2)at²

• v² = v₀² + 2aΔx

v = final velocity vector (m/s) v₀ = initial velocity (m/s) a = acceleration (m/s²) t = time (sec) Δx = displacement (m)

A vector is a quantity that has both magnitude and direction, such as velocity and displacement. A scalar lacks direction but has magnitude, such as mass and time. 

Problems that involve the usage of just one kinematics equations most likely won't show up on the MCQ portion of the test, and may show up on only part A of an FRQ, if at all. 

Generally, a good way to use kinematics equations or to solve physic questions in general is to first list given variables to determine which kinematic equation is most fit for the scenario. Make sure to double check your units! 

Example : A mass, initially at rest, travels a distance of 5km after 3 minutes on a frictionless surface. What was the acceleration of the mass?

To solve this problem -

• step 1  : identify known variables, and convert units to standard units (v₀ = 0 m/s, t = 3 minutes = 180 seconds, Δx = 5 km = 5000m)

• step 2 : identify unknown variables (a = ?)

• step 3 : figure out what equation to use, in this case it would be the second equation (Δx = v₀t + (1/2)at²)

• Plug and solve ! (5000 = 0 + (1/2)a(180)²) => a = 0.309 m/s²

Keep in mind that physic question scenarios introduced in early units can be altered by combining different factors in later units, and that kinematic equations can and should be used down the line! 

Within Unit 2, it's important to identify forces, as well as to be able to understand and draw Free Body Diagrams (FBD). FBD's will not only help significantly in figuring out MCQs, drawing these diagrams make up some portion of the FRQs. 

A force is a push or a pull. This may seem like something obvious, but there are different types of forces that are recognized in physics. Before learning those, it is important to understand the singular most important equation (in my opinion) of the entire AP Physics 1 course.

Fnet = ma

Fnet = Net force (N) m = mass (kg) a = acceleration (m/s²)

The important part of this equation is the F variable. Fnet = Net force, which can then be subdivided into the different types of force. Different forces will be used based on the differing scenarios, and sometimes there is more then one force acting on the object, hence the importance of drawing FBD's in order to recognize the order and what forces will be used. 

The different types of forces : 

T = tension N = normal force = mgcosθ Ff = friction = μN (μ is the friction coefficient) Fb = Buoyant force Fg = gravity = mg 

Fg can otherwise be known as weight. Weight and mass are two different quantities, where weight is a measure of the force of gravity on a mass. 

Normal force is always perpendicular to the point of contact of the mass and the surface, and is often cancelled out by the force of gravity. Buoyant force is always opposite of Fg, whereas friction is always opposite to the direction of movement of the mass. Friction can be divided into two 'subsections'; known as static friction and kinetic friction. Static friction is the amount of force required to keep an object from moving. Buoyant force is not important in Unit 2, and will be further explained in Unit 8. Tension is a pulling force, so it always acts away from the object. 

The direction of the forces not only determine how they are drawn in FBD's, but also how the equation is set up. If the forces are in the same direction, they share the same sign. If the forces are in opposite directions, then the two forces will have different signs. While this explanation is confusing, it will be clarified in the following scenarios. 

There are four common scenarios within Unit 2, that utilize kinematics equations along with the equations learned in Unit 2. 

Scenario 1 : The suitcase situation / Horizontal Pull

To fully understand this scenario, you must understand how to split force vectors. In the suitcase scenario (which can also be just a mass, a wagon, etc.), the force is pulled in a diagonal line in reference to the mass. This line can now be understood using trigonometric formulas and the pythagorean theorem.

 
Diagonal force A can be split into :
Aₓ = Acosθ

Aᵧ = Asinθ

If only given force components :
A = √Aₓ²+ Aᵧ²

𝛳 = 𝑡𝑎𝑛^−1(𝐴𝑦/𝐴𝑥)

The suitcase situation type of questions will often ask to identify the magnitude of a force. It is a similar concept with a horizontally pulled mass, there is just no need to split the components of force. Here's some example problems (with solutions) of both set ups. 

Example 1 : Samantha wants to drag her suitcase that has a mass of 30kg. She pulls it with a force of 100N at a 25 degree angle above ground. The static friction coefficient is 0.35, and the kinetic friction coefficient is 0.78. Calculate the magnitude of the normal force acting on the suitcase from the floor (highly suggest you draw a FBD to help you).

Scenario 2 : The elevator question

The elevator question only focuses on two forces. Simple, right? This question tests your understanding on the force of gravity versus tension. Keep in mind that while I may refer to this as the elevator question, it can come to you in forms such as a crane lifting a mass, a hot air balloon, etc. 

In order to solve these questions, you can think of it as a battle. Who's winning, gravity or tension? Oftentimes in these types of questions, they will ask you to solve within a scenario of a mass being lifted up or falling. It seems pretty straightforward that if the mass is falling, then gravity is winning and vice versa. However, the questions begin to require more thinking when sometimes on the MCQ they will ask questions such as : If an elevator is moving up but slowing down, which force is greatest? 

Another example question would ask you how much force is required to break the string, or the maximum mass a string can lift before breaking. 

Scenario 3 : Mass sliding down or up a ramp

This question is yet another scenario that requires you to understand the concept of splitting forces into separate components.

Scenario 4 : Uniform Circular Motion