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A cyclist travels from point A to point B in 10 min. During the first 2.0 min of her trip, she maintains a uniform acceleration of \(0.090 \mathrm{m} / \mathrm{s}^{2} .\) She then travels at constant velocity for the next 5.0 min. Next, she decelerates at a constant rate so that she comes to a rest at point \(\mathrm{B}\) 3.0 \(\mathrm{min}\) later. (a) Sketch the velocity-versus-time graph for the trip. (b) What is the acceleration during the last 3 min? (c) How far does the cyclist travel?

Short Answer

Expert verified
The acceleration during the last 3 minutes is -0.06 m/s虏, and the cyclist travels a total distance of 5832 meters during the 10-minute trip.

Step by step solution

01

List the given values and convert time to seconds

Given: Initial acceleration (a鈧) = 0.090 m/s虏 (first 2 minutes) Constant velocity (v鈧) = (for the next 5 minutes) Deceleration (a鈧) = (for the last 3 minutes) Total time (t) = 10 min = 600s First, convert the time for each phase of the trip into seconds: t鈧 (acceleration) = 2.0 min 脳 60 s/min = 120 s t鈧 (constant velocity) = 5.0 min 脳 60 s/min = 300 s t鈧 (deceleration) = 3.0 min 脳 60 s/min = 180 s
02

Sketch the velocity-time graph

The graph will show three distinct phases of the trip, each with their corresponding times: 1. Time interval 0 to 120 s: Uniform acceleration 2. Time interval 120 to 420 s: Constant velocity 3. Time interval 420 to 600 s: Deceleration The velocity-time graph will be a piecewise-linear graph, with uniform acceleration shown as a diagonal line starting from 0, constant velocity as a horizontal line, and deceleration as a diagonal line going back to the time axis. #b) What is the acceleration during the last 3 min?#
03

Calculate velocity after the acceleration phase

We'll use the first phase of the trip to find the maximum velocity (v鈧) achieved by the cyclist: Equation for uniformly accelerated motion: v = u + a鈧*t鈧 Here, u (initial velocity) = 0, since the cyclist starts from rest. So, v鈧 = a鈧 * t鈧 v鈧 = 0.090 m/s虏 * 120 s v鈧 = 10.8 m/s
04

Calculate the acceleration during the last 3 min

Since the cyclist comes to rest at the end of the deceleration phase, we can find the acceleration for the last 3 minutes using a similar equation: v = u + a鈧*t鈧 Here, v (final velocity) = 0, as the cyclist comes to rest. u (initial velocity) = v鈧 = 10.8 m/s t鈧 = 180 s (Last 3 min) 0 = 10.8 m/s + a鈧 * 180 s a鈧 = -10.8 m/s / 180 s a鈧 = -0.06 m/s虏 The acceleration during the last 3 minutes is -0.06 m/s虏. #c) How far does the cyclist travel?#
05

Calculate the distance traveled in each phase

We'll now calculate the distance traveled during each phase of the trip: 1. Phase 1 (uniform acceleration): Equation: s鈧 = ut鈧 + 0.5*a鈧*t鈧伮 s鈧 = 0 + 0.5*0.090 m/s虏*(120 s)虏 s鈧 = 648 m 2. Phase 2 (constant velocity): Equation: s鈧 = v鈧*t鈧 s鈧 = 10.8 m/s * 300 s s鈧 = 3240 m 3. Phase 3 (deceleration): Equation: s鈧 = v鈧*t鈧 + 0.5*a鈧*t鈧兟 s鈧 = 10.8 m/s * 180 s + 0.5*(-0.06 m/s虏)*(180 s)虏 s鈧 = 1944 m
06

Calculate the total distance traveled

Finally, we'll sum up the distances calculated for each phase to find the total distance traveled: Total distance (s) = s鈧 + s鈧 + s鈧 s = 648 m + 3240 m + 1944 m s = 5832 m The cyclist travels a total distance of 5832 meters during the 10-minute trip.

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Key Concepts

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

Uniform Acceleration
Understanding uniform acceleration is crucial when studying kinematics problems. It refers to a scenario where an object speeds up or slows down at a consistent rate over time. In our cyclist example, during the first phase of the trip, the cyclist experiences a uniform acceleration of 0.090 m/s虏. This means her speed increases by this amount each second for the entire 2-minute period.

Uniform acceleration can be visualized in a velocity-time graph as a straight line sloping upwards for acceleration and downwards for deceleration. If we know the time and the acceleration rate, as in the cyclist's case, we can use the equation of motion v = u + at to determine the change in velocity. In this equation, v is the final velocity, u is the initial velocity (which is zero for our cyclist when she begins accelerating), a is the acceleration, and t is the time.
Velocity-Time Graph
A velocity-time graph is an important tool in kinematics that displays how an object's velocity changes over time. In kinematics problems, such as the cyclist's journey, the graph is divided into sections representing different motion phases. The graph starts at the origin (0,0) since the cyclist starts from rest. As she accelerates, the line rises with a positive slope. When she travels at a constant velocity, the graph flatlines at the maximum velocity achieved. Finally, as the cyclist decelerates to a stop, the line slopes down back to the velocity axis.

The slopes on the velocity-time graph represent acceleration or deceleration, while the area under the graph can be used to calculate the distance traveled during a certain phase. This makes it a powerful visual aid in understanding and solving kinematics problems.
Equations of Motion
The equations of motion are essential tools for analyzing motion with uniform acceleration. These equations relate displacement (s), initial velocity (u), final velocity (v), acceleration (a), and time (t). In the context of our cyclist, these equations helped us calculate the distances traveled during various motion phases.

For the acceleration and deceleration phases, we used the equation s = ut + (1/2)at虏 鈥 since the initial velocity is zero, the first part drops off for the acceleration phase. The equation s = vt applies for the constant velocity phase. A key benefit of knowing the equations of motion is the ability to solve for any variable, as long as the other three are known, allowing us to piece together a complete picture of the motion described in the problem.

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Most popular questions from this chapter

A kangaroo can jump over an object 2.50 m high. (a) Considering just its vertical motion, calculate its vertical speed when it leaves the ground. (b) How long a time is it in the air?

The position of a particle moving along the \(x\) -axis varies with time according to \(x(t)=5.0 t^{2}-4.0 t^{3} \mathrm{m} .\) Find (a) the velocity and acceleration of the particle as functions of time, (b) the velocity and acceleration at \(t=2.0 \mathrm{s},(\mathrm{c})\) the time at which the position is a maximum, (d) the time at which the velocity is zero, and (e) the maximum position.

When given the acceleration function, what additional information is needed to find the velocity function and position function?

In 1967, New Zealander Burt Munro set the world record for an Indian motorcycle, on the Bonneville Salt Flats in Utah, of \(295.38 \mathrm{km} / \mathrm{h}\). The one-way course was \(8.00 \mathrm{km}\) long. Acceleration rates are often described by the time it takes to reach \(96.0 \mathrm{km} / \mathrm{h}\) from rest. If this time was 4.00 s and Burt accelerated at this rate until he reached his maximum speed, how long did it take Burt to complete the course?

(a) A light-rail commuter train accelerates at a rate of \(1.35 \mathrm{m} / \mathrm{s}^{2} .\) How long does it take to reach its top speed of 80.0 \(\mathrm{km} / \mathrm{h}\), starting from rest? (b) The same train ordinarily decelerates at a rate of \(1.65 \mathrm{m} / \mathrm{s}^{2} .\) How long does it take to come to a stop from its top speed? (c) In emergencies, the train can decelerate more rapidly, coming to rest from \(80.0 \mathrm{km} / \mathrm{h}\) in \(8.30 \mathrm{s}\). What is its emergency acceleration in meters per second squared?

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