# 5 | MCQ | Practice Sessions | AP Physics C: Mechanics

TLDRIn the AP Physics Practice Sessions for Mechanics, instructor Dee Dee Messer guides viewers through multiple-choice questions on gravitation and simple harmonic motion. She provides step-by-step solutions, encouraging students to pause and attempt questions themselves. The session covers topics such as calculating gravitational acceleration, understanding orbital mechanics, and analyzing spring dynamics, all aimed at preparing students for the AP exam.

###### Takeaways

- π The video is a practice session for AP Physics Mechanics, focusing on gravitation and simple harmonic motion.
- π©βπ« The instructor is Dee Dee Messer, an AP Physics C teacher at William Mason High School in Ohio.
- π Viewers have the option to download a PDF or answer questions as they appear on the screen.
- π The first topic discussed is the calculation of gravitational acceleration on the surface of a hypothetical Planet X, with given mass and diameter relative to Earth.
- π The script explains the process of deriving the gravitational acceleration formula and applying it to Planet X.
- π The second topic is about an astronaut in orbit around Earth, and the calculation of their acceleration due to gravity at a certain altitude.
- π The video covers the concept of centripetal acceleration and its relation to the gravitational force acting on an object in orbit.
- π A third scenario involves satellites in circular orbits at different distances from a planet and the relationship between their orbital speeds.
- π The script introduces a new planet with twice the mass of Earth but the same surface gravity, leading to a calculation of its radius.
- π The video also addresses the conservation of angular momentum in elliptical orbits and its implications for the speed of a comet at different positions.
- π The final topics include simple harmonic motion, with examples of a spring in vertical position and the calculation of spring constant and potential energy.
- π The session concludes with a discussion on differential equations for simple harmonic oscillators and the application of Newton's second law.

###### Q & A

### What is the main focus of the AP Physics Practice Session conducted by Dee Dee Messer?

-The main focus of the session is to practice multiple choice questions on the topics of gravitation and simple harmonic motion.

### How does Dee Dee Messer suggest students can follow along with the practice session?

-Students can either download the PDF linked in the video to have a paper copy to follow along or do the questions ahead of time. Alternatively, they can pause the video when a new question is shown, try to answer it, and then resume to see the final answer.

### What is the acceleration due to gravity at the surface of Planet X, which has 1/10 the mass and 1/2 the diameter of Earth?

-The acceleration due to gravity at the surface of Planet X is 4 meters per second squared.

### What is the approximate acceleration of an astronaut 300 kilometers above the Earth's surface?

-The approximate acceleration of the astronaut is 9 meters per second squared.

### What is the speed required for a satellite to maintain a circular orbit at a distance of 2R from the center of a planet, if its initial speed was V0 at a distance R?

-The required speed is V0 divided by the square root of 2.

### What is the radius of a newly discovered planet with twice the mass of Earth but the same surface gravity as Earth?

-The radius of the new planet is the square root of 2 times the radius of Earth.

### What is the ratio of the speed of a comet at position 1 to its speed at position 2 in an elliptical orbit, where position 1 is 10 times as far from the Sun as position 2?

-The ratio of the speed of the comet at position 1 to its speed at position 2 is 1/10.

### At which time is the upward velocity of an object attached to a vertically hanging spring the greatest?

-The upward velocity is greatest at 0.25 seconds.

### What is the spring constant of an ideal spring with a 0.4 kilogram object attached, given that the period of oscillation is 1 second?

-The spring constant is approximately 16 Newtons per meter.

### What is the possible potential energy function for a conservative force given by F = -kx^3?

-The potential energy function is U = 1/4 kx^4.

### What is the differential equation that correctly describes Newton's second law for a simple harmonic oscillator of mass m and force constant k?

-The differential equation is m(dΒ²x/dtΒ²) = -kx.

###### Outlines

##### π AP Physics Practice Session Introduction

Dee Dee Messer, an AP Physics C teacher, introduces an AP Physics practice session focusing on gravitation and simple harmonic motion. Viewers can either download a PDF for reference or attempt to answer the questions as they are presented on-screen. The session begins with a question about calculating the acceleration due to gravity on Planet X, given its mass and diameter relative to Earth's. The teacher uses the gravitational force equation to derive the answer, which is 4 meters per second squared. Subsequent questions involve an astronaut in orbit, the speed of a satellite at different distances from a planet, and the radius of a newly discovered planet with twice Earth's mass but the same surface gravity.

##### π Gravitational and Orbital Mechanics Questions

This section continues the AP Physics practice with questions on the gravitational force affecting an astronaut in orbit 300 kilometers above Earth and the speed required for a satellite to maintain a circular orbit at varying distances from a planet. The teacher explains how to use the gravitational force equation to find the astronaut's acceleration and the satellite's speed, emphasizing the importance of understanding the changing radius and its effect on gravitational acceleration. The discussion also includes a question about the ratio of velocities and kinetic energy of a comet in an elliptical orbit around the Sun, applying Kepler's second law and conservation of angular momentum.

##### π Simple Harmonic Motion and Conservative Forces

The final part of the script transitions from gravitational topics to simple harmonic motion, discussing a vertically hanging spring with an attached mass. The teacher explains how to determine the spring constant using the period of oscillation and the mass of the object. A new scenario introduces a one-dimensional conservative force expressed as a function of position, leading to the calculation of a potential energy function. The session concludes with a question on writing a differential equation for Newton's second law in the context of a simple harmonic oscillator, highlighting the relationship between force, mass, acceleration, and displacement.

###### Mindmap

###### Keywords

##### π‘AP Physics Practice Sessions

##### π‘Gravitation

##### π‘Simple Harmonic Motion

##### π‘Acceleration Due to Gravity

##### π‘Orbit

##### π‘Centripetal Acceleration

##### π‘Spring Constant

##### π‘Conservative Force

##### π‘Potential Energy

##### π‘Differential Equation

##### π‘Newton's Second Law

###### Highlights

Introduction to AP Physics Practice Sessions for Mechanics with Dee Dee Messer.

Two options provided for engaging with the practice questions: downloading the PDF or pausing the video to answer.

Explanation of calculating acceleration due to gravity on Planet X with given mass and diameter ratios to Earth.

Derivation of the gravitational force equation and its simplification for Planet X.

Calculation of an astronaut's acceleration in a circular orbit 300 km above Earth's surface.

Elimination of incorrect choices based on the understanding of gravitational force and orbit dynamics.

Method to determine the required speed for a satellite in a new circular orbit at 2R distance from a planet.

Use of centripetal acceleration and gravitational force equations to solve for the satellite's speed.

Determination of a new planet's radius given its mass is twice that of Earth and has the same surface gravity.

Application of Newton's universal gravitational force equation to find the radius of the new planet.

Analysis of an elliptical orbit scenario involving a comet moving around the Sun with positions at different distances.

Calculation of the speed ratio of the comet at two positions in its elliptical orbit.

Understanding of angular momentum conservation and its application to find the speed ratio.

Determination of the comet's kinetic energy at position 2, considering its maximum speed at closest approach to the Sun.

Transition from gravitation to simple harmonic motion with an example of a vertically hanging spring.

Identification of when the upward velocity of an object attached to a spring is the greatest.

Calculation of the spring constant using the period of oscillation and the mass of the object.

Introduction of a one-dimensional conservative force function and the task to find a corresponding potential energy function.

Integration of the force function to derive the potential energy function for a conservative force.

Formulation of a differential equation that describes Newton's second law for a simple harmonic oscillator.

Emphasis on the importance of practice for success in the AP Physics exam.

###### Transcripts

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