Newton's Second Law Exam Question: Two-body systems Pulley practice

Miss Martins Maths and Science

29 Feb 202428:15

EducationalLearning

32 Likes 10 Comments

TLDRIn this educational video, Miss Martins guides high school students through a complex physics problem involving Newton's second law and a pulley system. The video begins with an introduction to the topic and the importance of understanding key concepts such as the normal force. The problem presented involves two blocks with masses of 5 kg and 2 kg connected by a string running over a frictionless pulley. The 5 kg block is subject to a kinetic frictional force of 10 N and an applied force at an angle, while the 2 kg block is only affected by its weight and the tension in the string. Miss Martins emphasizes the need for a free body diagram to visualize all forces acting on the blocks and breaks down the problem step by step, using Newton's second law to calculate the tension in the string and the magnitude of the applied force. She also calculates the coefficient of kinetic frictional force on the 5 kg block, demonstrating the process of resolving forces into components and using trigonometric relationships. The video concludes with a reminder to subscribe for more physics content and a promise of future videos to aid students in their studies.

Takeaways

📚 Start by understanding the basics: The video emphasizes the importance of knowing definitions, such as 'normal force,' which is the force exerted by a surface on an object it is in contact with, perpendicular to the surface.
🎯 Identify the forces involved: The video explains how to identify and represent the forces acting on objects, including tension, weight, normal force, applied force, and frictional force in a free body diagram.
📐 Use a ruler for accuracy: When drawing forces at an angle, it's crucial to use a ruler for precision, which aids in solving the problem accurately.
🔍 Break down forces into components: The video demonstrates how to resolve forces into horizontal (parallel) and vertical (perpendicular) components, which is essential for solving complex problems.
⚖️ Tension is consistent: The tension in the string is the same for both blocks connected by the string, which is a key point in solving the problem.
↗️ Choose the right approach: The video suggests using the 2 kg block to calculate tension because all forces acting on it are known, making the calculation straightforward.
🔢 Apply Newton's second law: The net force (Fnet) equals mass times acceleration (ma), which is used to calculate the unknown forces in the system.
🧮 Solve for the unknowns: The video walks through solving for the applied force by using its components and the known forces, leveraging trigonometric relationships.
⚖️ Coefficient of kinetic friction: The video explains how to calculate the coefficient of kinetic friction by using the known frictional force and the calculated normal force.
📉 Don't forget units and directions: The video reminds viewers to include the correct units and directions for forces when solving problems and to follow the formula sheet precisely.
📈 Marking scheme understanding: The video provides insight into how marks are awarded for different parts of the problem, emphasizing the need for clear labeling, accurate diagrams, and correct formula application.

Q & A

What is the topic of the video?
-The video is about Newton's second law and a pulley question involving two blocks of different masses connected by a string over a frictionless pulley.
What is the mass of the two blocks in the problem?
-The masses of the blocks are 5 kg and 2 kg respectively.
What is the acceleration of the system of blocks?
-The system of blocks accelerates to the right at 2 m/s squared.
What is the kinetic frictional force on the 5 kg block?
-The kinetic frictional force on the 5 kg block is 10 Newtons.
What is the normal force?
-The normal force is the force or the component of a force which a surface exerts on an object in contact with it, and which is perpendicular to the surface.
Why is it important to draw a free body diagram when solving a Newton's law question?
-Drawing a free body diagram helps visualize all the forces acting on an object, assists in breaking down forces into components, and is essential for applying Newton's laws correctly to find unknowns like tension or applied force.
How can you find the tension in the string using Newton's second law?
-You can find the tension in the string by applying Newton's second law to the 2 kg block, considering the forces acting in the vertical direction (tension and weight), and solving for the net force (F_net = m*a).
What is the applied force acting on the 5 kg block?
-The applied force is a force that acts at a 20-degree angle to the horizontal and is responsible for the block's acceleration. Its magnitude is unknown and needs to be calculated using the provided information.
How do you calculate the applied force magnitude?
-To calculate the applied force magnitude, you use the horizontal (X) component of the applied force, which is found using the tension in the string and the frictional force, and apply trigonometric functions to resolve the applied force into its components.
What is the coefficient of kinetic frictional force?
-The coefficient of kinetic frictional force is found by dividing the kinetic frictional force by the normal force. It is a dimensionless quantity that represents the friction between two surfaces in motion.
Why is it necessary to calculate the normal force before finding the coefficient of kinetic friction?
-The normal force is necessary because it, along with the weight of the block and the perpendicular component of the applied force, must sum to zero in the vertical direction since there is no vertical acceleration. This is required to use the formula for the coefficient of kinetic friction.
How should you label your free body diagrams?
-You should label your free body diagrams with clear and distinct labels for each force, including the direction of the force. Ensure that the diagram is large enough to accommodate all labels for clarity and avoid losing marks due to an unclear diagram.

Outlines

00:00

📚 Introduction to Newton's Second Law and Pulley Systems

Miss Martins welcomes grade 11 and 12 students to a physics video focusing on Newton's second law, particularly in the context of a pulley question involving inclined forces, adding complexity. She emphasizes the importance of understanding the tension in the strings, the acceleration of the system, and the forces acting on the blocks. The video aims to guide students on how to approach such problems and succeed in their exams.

05:02

📐 Free Body Diagrams and Normal Force Definition

The video instructs students to draw free body diagrams for the 5 kg block, highlighting the need for accuracy and labeling of forces. It also explains the concept of normal force, which is the force exerted by a surface that an object is in contact with, perpendicular to the surface. The importance of studying all definitions from the official physical sciences exam guidelines is stressed.

10:04

🔍 Resolving Forces and Calculating Tension

Miss Martins demonstrates how to resolve forces into components, specifically for the applied force acting at a 20° angle. She uses the 2 kg block's free body diagram to calculate the tension in the string, employing Newton's second law of motion. The process involves summing the vertical forces (tension and weight) and solving for tension, which acts upwards.

15:04

🧮 Finding the Applied Force and its Components

The video moves on to calculating the magnitude of the applied force acting on the 5 kg block. It uses trigonometric relationships to find the horizontal (F_applied X) and vertical (F_applied Y) components of the applied force. The focus is on using the horizontal components to find the applied force since the vertical components involve unknowns like the normal force.

20:05

🎯 Calculating the Coefficient of Kinetic Friction

The final part of the video deals with calculating the coefficient of kinetic frictional force on the 5 kg block. It involves first determining the normal force by considering all upward forces (FN, FG, and the Y component of F_applied). Then, using the known frictional force and the calculated normal force, the coefficient of kinetic friction is found using the formula provided. Accuracy in following the formula as stated in the exam guidelines is emphasized.

25:08

📝 Conclusion and Encouragement for Further Learning

Miss Martins concludes the video by summarizing how to score marks for each question, emphasizing the importance of correct formula usage, substitution, and providing the answer without units for the coefficient of friction. She encourages students to find more videos in her Newton playlist for further learning and looks forward to their continued engagement in future videos.

Mindmap

Keywords

💡Newton's Second Law

Newton's Second Law of Motion states that the acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass. It is fundamental to classical mechanics and is used in the video to analyze the forces acting on the blocks in the pulley system. The law is applied when calculating the tension in the string and the applied force on the 5 kg block.

💡Pulley System

A pulley system is a mechanical device that supports the movement and transportation of heavy objects by changing the direction of the force applied. In the video, the pulley system is used to connect two blocks of different masses, creating a scenario where the forces and motion of both blocks are interrelated, which is central to the physics problem being solved.

💡Tension

Tension refers to the force transmitted through a string, rope, or cable when it is pulled tight by opposing forces. In the context of the video, tension is the force acting on the blocks connected by the string over the pulley, and it is a key variable in determining the motion and acceleration of the system.

💡Frictional Force

Frictional force is the resistance that one surface or object encounters when moving over another. It plays a significant role in the video as it opposes the motion of the 5 kg block and is given as 10 N. The calculation of the coefficient of kinetic friction is a part of the problem-solving process in the video.

💡Free Body Diagram

A free body diagram is a graphical representation that shows all the forces acting on an object in a given situation. It is a crucial tool in physics for visualizing and solving problems involving forces. In the video, free body diagrams are drawn for both the 5 kg and 2 kg blocks to analyze the forces acting on them.

💡Normal Force

The normal force is the force exerted by a surface that supports the weight of an object resting on it, always perpendicular to the surface of contact. It is an essential concept in the video as it helps in calculating the net force acting on the 5 kg block and is used to find the coefficient of kinetic friction.

💡Kinetic Friction

Kinetic friction, also known as dynamic friction, is the frictional force that resists the relative motion between two objects in motion. It is calculated using the formula F_friction = μ * F_normal, where μ is the coefficient of kinetic friction. The video explains how to determine μ for the 5 kg block using the given frictional force and the calculated normal force.

💡Coefficient of Kinetic Friction

The coefficient of kinetic friction (μ) is a dimensionless scalar that represents the ratio of the frictional force to the normal force. It is a material property and is used in the video to find the relationship between the frictional force acting on the 5 kg block and the normal force.

💡Acceleration

Acceleration is the rate of change of velocity over time. It is a vector quantity that describes the change in velocity an object experiences. In the video, the system of blocks accelerates to the right at 2 m/s², which is used to apply Newton's Second Law and find the unknown forces in the system.

💡Force Components

Force components refer to the separate parts of a force when it is broken down into orthogonal (perpendicular) parts. In the video, the applied force on the 5 kg block is at an angle, so it is resolved into horizontal (parallel) and vertical (perpendicular) components to facilitate the calculation of the tension in the string.

💡Mass

Mass is a measure of the amount of matter in an object and is a property that affects its resistance to acceleration (inertia) and the strength of its gravitational attraction to other masses. In the video, the masses of the two blocks (5 kg and 2 kg) are essential for calculating the forces and accelerations involved in the pulley system.

Highlights

Miss Martins introduces a video on Newton's 2nd law with a focus on a pulley system question.

The video includes an analysis of a complex exam question involving inclined forces and a system of connected blocks.

A detailed explanation of the term 'normal force' is provided, emphasizing its importance in physics.

Miss Martins demonstrates how to create a free body diagram for the 5 kg block, highlighting the need for accuracy and clarity.

The importance of understanding the direction of forces, such as tension and friction, is emphasized in the context of Newton's laws.

A method to calculate the tension in the string using Newton's second law is presented.

The video explains how to resolve forces into components to solve for unknown quantities, such as the applied force.

Miss Martins shows how to find the applied force on the 5 kg block by considering the horizontal and vertical components.

The calculation of the coefficient of kinetic frictional force is covered, using a step-by-step approach.

The necessity of including the correct formula and units when calculating physical quantities is stressed.

Miss Martins advises on the strategic selection of which block to use for calculations based on the forces involved.

The video provides a comprehensive breakdown of how to approach and solve a complex physics problem step by step.

The importance of drawing a free body diagram even when it's not explicitly asked for is discussed for better understanding.

A reminder is given to always use the formula as it appears on the official formula sheet to avoid marking errors.

The video concludes with a summary of how to earn marks for each step of the problem-solving process in an exam setting.

Miss Martins encourages students to watch more videos in the Newton's Law playlist for a deeper understanding of the subject.

The video serves as a practical guide for high school students preparing for physics exams, particularly those involving pulley systems.

Transcripts

Browse More Related Video

Work and Kinetic Energy - Physics

Treating systems (the hard way) | Forces and Newton's laws of motion | Physics | Khan Academy

Finding the Tension and Acceleration for a Two Mass Pulley (with Friction)

2015 AP Physics 1 free response 1b

2015 AP Physics 1 free response 1a

Net Force Physics Problems With Frictional Force and Acceleration

Related Tags

Newton's Law Physics Pulley System Friction Applied Force Tension Force Exam Preparation Educational Video High School Science Education Problem Solving