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In a marathon race Chad is out in front, running due north at a speed of 4.00 m/s. John is 95 m behind him, running due north at a speed of 4.50 m/s. How long does it take for John to pass Chad?

Short Answer

Expert verified
It takes 190 seconds for John to pass Chad.

Step by step solution

01

Understand the Problem

Chad and John are both running northward. Chad is 95 meters ahead of John and runs at 4.00 m/s. John is running faster at 4.50 m/s. We need to find the time it takes for John to catch up and pass Chad.
02

Define Relative Motion

To determine when John catches Chad, we consider their relative speeds. John's speed relative to Chad is the difference in their speeds: \( v_{relative} = 4.50 \text{ m/s} - 4.00 \text{ m/s} = 0.50 \text{ m/s} \). This means John gains 0.50 meters on Chad every second.
03

Set Up the Equation

John needs to make up 95 meters to catch Chad. Using the relative speed, set up the equation for time \( t \): \( d = v_{relative} \times t \), where \( d = 95 \text{ m} \) and \( v_{relative} = 0.50 \text{ m/s} \).
04

Solve for Time

Solve the equation \( 95 \text{ m} = 0.50 \text{ m/s} \times t \) for \( t \). Dividing both sides by 0.50 m/s, we get \( t = \frac{95}{0.50} = 190 \text{ s} \).
05

Double Check the Calculation

Verify the calculation: Multiply \( 0.50 \text{ m/s} \times 190 \text{ s} \) to ensure it equals 95 meters, confirming that the time taken is correct.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Problem Solving
Solving physics problems often begins with carefully understanding the scenario at hand. For this particular exercise, the key to solving the problem was realizing the relationship between the two runners, Chad and John. Identifying this relationship allows us to determine how quickly John gains ground on Chad.

This method often involves breaking down the problem into manageable parts:
  • Clearly outline what is given: Chad and John's speeds and the distance between them.
  • Determine what needs to be found: The time for John to pass Chad.
  • Utilize the concept of relative motion to devise a plan.
Breaking problems down in this way aids in converting the situation into mathematical expressions. As you gain practice, these steps will become second nature and will enable you to tackle increasingly complex questions.
Kinematics
Kinematics is the branch of mechanics that deals with the motion of objects without considering the forces that cause the motion. In this exercise, understanding kinematics was crucial.

We focused on the straight-line motion of two runners. Both are traveling north at constant velocities, which simplifies the problem. We didn't need to worry about changes in speed or direction.

Relative Speed in Kinematics

In kinematics, relative speed is a common concept, particularly when considering how two objects move with respect to each other. For John and Chad, the relative speed of 0.50 m/s told us how quickly John was closing in on Chad.

By focusing solely on their motion, kinematics allowed us to predict when and where events occurred鈥攍ike when one runner would pass the other.
Speed and Velocity
Speed and velocity are fundamental in understanding motion. Although these terms are often used interchangeably in everyday language, they have distinct meanings in physics.

**Speed** is a scalar quantity that refers to how fast an object is moving. It only considers the magnitude of the motion.
  • In our exercise, Chad's speed was 4.00 m/s, while John's was 4.50 m/s.
**Velocity**, however, is a vector quantity, which means it includes both magnitude and direction. The fact that both runners were moving due north added an extra layer of simplicity; their velocities differed only in magnitude in this problem.

Relative Velocity

The concept of relative velocity allowed us to see the motion from one runner's perspective. By subtracting Chad's speed from John's, we obtained John's relative speed compared to Chad's, which was crucial in solving the problem.

This concept shows how changing reference points can simplify solving motion problems and are beneficial for various physics applications.

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