Mechanics Quiz for AP Physics B & C (page 2)
Are you getting ready to take the AP physics exam? Before you begin studying, find out what you know and you don't know with these four fundamental quizzes: Mechanics Quiz for AP Physics B & C , Thermodynamics and Fluid Mechanics Quiz for AP Physics B & C , Electricity and Magnetism Quiz for AP Physics B & C , and Waves, Optics, Atomic and Nuclear Physics Quiz for AP Physics B & C
It's okay if you didn't get every question on all of the fundamentals quizzes correct. The whole point of these quizzes is for you to determine where to focus your study.
It's a common mistake to "study" by doing 20 problems on a topic on which you are already comfortable. But that's not studying … that's a waste of time. You don't need to drill yourself on topics you already understand! It's also probably a mistake to attack what for you is the toughest concept in physics right before the exam. Virtually every student has that one chapter they just don't get, however hard they try. That's okay … (as long as it's only one chapter.)
These fundamentals quizzes can tell you exactly what you should and should not study. Did you give correct answers with full confidence in the correctness of your response? In that case, you're done with that topic. No more work is necessary. The place to focus your efforts is on the topics where either you gave wrong answers that you thought were right, or right answers that you weren't really sure about.
Here is the mechanics quiz.
- What is the mass of a block with weight 100 N?
- Give the equations for two types of potential energy, identifying each.
- When an object of mass m is on an incline of angle θ, one must break the weight of an object into components parallel to and perpendicular the incline.
- What is the component of the weight parallel to the incline? _____
- What is the component of the weight perpendicular to the incline? _____
- Write two expressions for work, including the definition of work and the work-energy principle.
- Quickly identify as a vector or a scalar:
- Name at least four things that can NEVER go on a free-body diagram.
- Write two expressions for impulse. What are the units of impulse?
- In what kind of collision is momentum conserved? In what kind of collision is kinetic energy conserved?
- What is the mass of a block with weight W?
- A ball is thrown straight up. At the peak of its flight, what is the ball's acceleration? Be sure to give both magnitude and direction.
- A mass experiences a force vector with components 30 N to the right, 40 N down. Explain how to determine the magnitude and direction (angle) of the force vector.
- Write the definition of the coefficient of friction, μ. What are the units of μ?
- How do you find acceleration from a velocity-time graph?
- How do you find displacement from a velocity-time graph?
- How do you find velocity from a position-time graph?
- An object has a positive acceleration. Explain briefly how to determine whether the object is speeding up, slowing down, or moving with constant speed.
- Given the velocity of an object, how do you tell which direction that object is moving?
- When is the gravitational force on an object mg? When is the gravitational force Gm1m2 /r2?
- What is the direction of the net force on an object that moves in a circle at constant speed?
- Under what conditions is the equation x – x0 = v0t + at2 valid? Give a specific situation in which this equation might seem to be valid, but is NOT.
_____ acceleration _____ force _____ momentum
_____ velocity _____ speed _____ displacement
_____ work _____ mass _____ kinetic energy
- Weight is mg. So, mass is weight divided by g = 100 N/(10 N/kg) = 10 kg.
- PE = mgh, gravitational potential energy;
- mg sin θ is parallel to the incline.
- mg cos θ is perpendicular to the incline.
- The definition of work is work = force times parallel displacement
- vectors: acceleration, force, momentum, velocity, displacement
- Only forces acting on an object and that have a single, specific source can go on freebody diagrams. Some of the things that cannot go on a free-body diagram but that students often put there by mistake:
- Impulse is force times time interval, and also change in momentum. Impulse has units either of Newton · seconds or kilogram · meters/second.
- Momentum is conserved in all collisions. Kinetic energy is conserved only in elastic collisions.
- Using the reasoning from question #1, if weight is mg, then m = W/g.
- The acceleration of a projectile is always g; i.e., 10 m/s2, downward. Even though the velocity is instantaneously zero, the velocity is still changing, so the acceleration is not zero. [By the way, the answer "–10 m/s2" is wrong unless you have clearly and specifically defined the down direction as negative for this problem.]
- The magnitude of the resultant force is found by placing the component vectors tip-totail. This gives a right triangle, so the magnitude is given by the Pythagorean theorem, 50 N. The angle of the resultant force is found by taking the inverse tangent of the vertical component over the horizontal component, tan–1(40/30). This gives the angle measured from the horizontal.
- Acceleration is the slope of a velocity-time graph.
- Displacement is the area under a velocity-time graph (i.e., the area between the graph and the horizontal axis).
- Because acceleration is not zero, the object cannot be moving with constant speed. If the signs of acceleration and velocity are the same (here, if velocity is positive), the object is speeding up. If the signs of acceleration and velocity are different (here, if velocity is negative), the object is slowing down.
- An object always moves in the direction indicated by the velocity.
- Near the surface of a planet, mg gives the gravitational force. Newton's law of gravitation, Gmm/r2, is valid everywhere in the universe. (It turns out that g can be found by calculating GMplanet/Rplanet 2, where Rplanet is the planet's radius.)
- An object in uniform circular motion experiences a centripetal, meaning "center seeking," force. This force must be directed to the center of the circle.
- This and all three kinematics equations are valid only when acceleration is constant. So, for example, this equation can NOT be used to find the distance travelled by a mass attached to a spring. The spring force changes as the mass moves; thus, the acceleration of the mass is changing, and kinematics equations are not valid. (On a problem where kinematics equations aren't valid, conservation of energy usually is what you need.)
PE = 1/2kx2, potential energy of a spring.
The work-energy principle states that net work = change in kinetic energy
scalars: speed, work, mass, kinetic energy
motion mass acceleration ma
centripetal force velocity inertia
friction force divided by normal force μ has no units.
Velocity is the slope of a position-time graph. If the position-time graph is curved, then instantaneous velocity is the slope of the tangent line to the graph.
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