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Ch 02: Kinematics in One Dimension
Knight Calc - Physics for Scientists and Engineers 5th Edition
Knight Calc5th EditionPhysics for Scientists and EngineersISBN: 9780137344796Not the one you use?Change textbook
Chapter 2, Problem 11

FIGURE EX2.8 showed the velocity graph of blood in the aorta. What is the blood's acceleration during each phase of the motion, speeding up and slowing down?

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1
Step 1: Understand the graph. The graph shows velocity (Vx) on the y-axis and time (t) on the x-axis. The motion is divided into three stages: Stage 1 (speeding up), Stage 2 (slowing down), and Stage 3 (constant velocity). Acceleration is the rate of change of velocity with respect to time, calculated as a = Δv / Δt.
Step 2: Analyze Stage 1 (speeding up). In this stage, velocity increases from 0 m/s to 6 m/s over a time interval of 2 seconds. Use the formula for acceleration: a = (v_final - v_initial) / (t_final - t_initial). Substitute v_initial = 0 m/s, v_final = 6 m/s, t_initial = 0 s, and t_final = 2 s.
Step 3: Analyze Stage 2 (slowing down). In this stage, velocity decreases from 6 m/s to 4 m/s over a time interval of 4 seconds (from t = 2 s to t = 6 s). Use the same formula for acceleration: a = (v_final - v_initial) / (t_final - t_initial). Substitute v_initial = 6 m/s, v_final = 4 m/s, t_initial = 2 s, and t_final = 6 s.
Step 4: Analyze Stage 3 (constant velocity). In this stage, velocity remains constant at 4 m/s from t = 6 s to t = 10 s. Since there is no change in velocity, the acceleration is zero. This can be confirmed using the formula: a = (v_final - v_initial) / (t_final - t_initial), where v_initial = v_final = 4 m/s.
Step 5: Summarize the results. Calculate the acceleration for each stage using the formulas provided. Stage 1 has positive acceleration (speeding up), Stage 2 has negative acceleration (slowing down), and Stage 3 has zero acceleration (constant velocity).

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Velocity

Velocity is a vector quantity that describes the rate of change of an object's position with respect to time. It has both magnitude and direction, which means it indicates how fast an object is moving and in which direction. In the context of the blood flow in the aorta, the velocity graph shows how the speed of blood changes over time during different phases of its motion.
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Acceleration

Acceleration is the rate of change of velocity over time. It can be positive (speeding up) or negative (slowing down). In the velocity-time graph provided, the slope of the line segments indicates the acceleration during each phase: a steep positive slope indicates increasing speed, while a negative slope indicates decreasing speed. Flat segments indicate constant velocity, meaning zero acceleration.
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Slope of a Graph

The slope of a graph represents the relationship between two variables. In a velocity-time graph, the slope corresponds to acceleration. A positive slope indicates acceleration (speeding up), a negative slope indicates deceleration (slowing down), and a zero slope indicates constant velocity. Analyzing the slopes in the given graph allows us to determine the acceleration of blood during each phase of its motion.
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