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The acceleration of a particle is directly proportional to the square of the time \(t .\) When \(t=0\), the particle is at \(x=24 \mathrm{m}\). Knowing that at \(t=6 \mathrm{s}, x=96 \mathrm{m}\) and \(v=18 \mathrm{m} / \mathrm{s},\) express \(x\) and \(v\) in terms of \(t .\)

Short Answer

Expert verified
Velocity: \( v(t) = \frac{t^3}{3} - 54 \); Position: \( x(t) = \frac{t^4}{12} - 54t + 24 \).

Step by step solution

01

Identify Given Information

The problem states that the acceleration of the particle, \( a \), is proportional to \( t^2 \). At \( t = 0 \), \( x = 24 \) m. At \( t = 6 \) s, \( x = 96 \) m and \( v = 18 \) m/s.
02

Express Acceleration in Functional Form

Since acceleration \( a \) is proportional to \( t^2 \), we can write it as \( a = k t^2 \) where \( k \) is a constant of proportionality.
03

Integrate to Find Velocity as a Function of Time

Integrate the acceleration function to find velocity: \( \int k t^2 \, dt = \frac{k t^3}{3} + C_v \). This gives us the velocity function \( v(t) = \frac{k t^3}{3} + C_v \).
04

Use Initial Condition for Velocity

At \( t = 6 \) s, \( v = 18 \) m/s. Plug these values into the velocity equation: \( 18 = \frac{k (6)^3}{3} + C_v \). Simplifying gives \( 18 = 72k + C_v \).
05

Integrate to Find Position as a Function of Time

Integrate the velocity function to find position: \( \int \left( \frac{k t^3}{3} + C_v \right) dt = \frac{kt^4}{12} + C_v t + C_x \). This gives the position function \( x(t) = \frac{kt^4}{12} + C_v t + C_x \).
06

Use Initial Condition for Position

At \( t = 0 \), \( x = 24 \) m. Using this in the equation \( x(t) = \frac{kt^4}{12} + C_v t + C_x \) gives \( 24 = C_x \).
07

Solve for Unknown Constant \(k\)

Using \( t = 6 \), \( x = 96 \) m: \( 96 = \frac{k (6)^4}{12} + C_v(6) + 24 \). This simplifies to \( 96 = 18k + 6C_v + 24 \) leading to \( 18k + 6C_v = 72 \).
08

Solve Simultaneous Equations

From steps 4 and 7, use the equations: \( 72k + C_v = 18 \) and \( 18k + 6C_v = 72 \). Solve simultaneously to find \( k = 1 \) and \( C_v = -54 \).
09

Write Final Equations for Position and Velocity

Substitute \( k = 1 \) and \( C_v = -54 \) into the expressions for \( v(t) \) and \( x(t) \). Thus, \( v(t) = \frac{t^3}{3} - 54 \) and \( x(t) = \frac{t^4}{12} - 54t + 24 \).

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Key Concepts

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

Particle Motion
In kinematics, particle motion describes how a particle moves through space over time. Understanding the particle's motion involves knowing the particle's position, velocity, and acceleration at any given time. This is often expressed using mathematical functions.
In this problem, we are focused on a particle that starts at a position of 24 meters when time is zero. By the time 6 seconds have passed, it has moved to a position of 96 meters with a velocity of 18 m/s. We need to determine how its position and velocity change continuously over time.
This requires setting up equations for position and velocity functions. These functions help map out the motion of the particle as it both speeds up and slows down, reacting to the forces acting on it.
Acceleration
Acceleration describes how quickly the velocity of a particle changes over time. In this scenario, the acceleration is directly proportional to the square of time, represented mathematically as \( a = k \cdot t^2 \), where \( k \) is a constant.
This means as time squares and grows larger, the acceleration increases more dramatically. Essentially, the long the time, the greater the acceleration.Knowing this relationship allows us to integrate acceleration to find the velocity function. By doing so, we can understand how the velocity changes at any given instant.
Acceleration is crucial as it gives insight not only into the speed but also the direction of a particle's motion over time.
Velocity
Velocity is a vector that describes the speed and direction of a particle's motion. For our problem, the velocity function can be found by integrating the acceleration function \( a = k \cdot t^2 \) over time, leading to \( v(t) = \frac{k t^3}{3} + C_v \).
At \( t = 6 \) seconds, we know that the velocity is 18 meters per second. This specific information allows us to solve for constants in our velocity function, like \( k \) and \( C_v \). By doing so, we make the velocity equation unique to this specific particle's scenario. Ultimately, velocity functions provide detailed insights into how the particle's speed and direction change over time.
Position Functions
Position functions tell us where a particle is located at any given time. To find the position function \( x(t) \), we integrate the velocity function \( v(t) \).
This operation gives us \( x(t) = \frac{kt^4}{12} + C_v t + C_x \), where \( C_x \) is another constant determined by the initial condition of the particle's position. Using the condition at \( t = 0 \) that \( x = 24 \), we find \( C_x = 24 \).
In situations like this, initial conditions are crucial as they allow us to find the specific constants, making the position function accurately describe the particle's path. We can then see how our particle moves along a line, curve, or in any trajectory defined by this position function.

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Most popular questions from this chapter

An elevator starts from rest and moves upward, accelerating at a rate of \(1.2 \mathrm{m} / \mathrm{s}^{2}\) until it reaches a speed of \(7.8 \mathrm{m} / \mathrm{s}\), which it then maintains. Two seconds after the elevator begins to move, a man standing \(12 \mathrm{m}\) above the initial position of the top of the elevator throws a ball upward with an initial velocity of \(20 \mathrm{m} / \mathrm{s}\). Determine when the ball will hit the elevator.

As part of a department store display, a model train \(D\) runs on a slight incline between the store's up and down escalators. When the train and shoppers pass point \(A,\) the train appears to a shopper on the up escalator \(B\) to move downward at an angle of \(22^{\circ}\) with the horizontal, and to a shopper on the down escalator \(C\) to move upward at an angle of \(23^{\circ}\) with the horizontal and to travel to the left. Knowing that the speed of the escalators is \(3 \mathrm{ft} / \mathrm{s}\), determine the speed and the direction of the train.

A brass (nonmagnetic) block \(A\) and a steel magnet \(B\) are in equilibrium in a brass tube under the magnetic repelling force of another steel magnet \(C\) located at a distance \(x=0.004 \mathrm{m}\) from \(B\). The force is inversely proportional to the square of the distance between \(B\) and \(C .\) If block \(A\) is suddenly removed, the acceleration of block \(B\) is \(a=-9.81+k / x^{2},\) where \(a\) and \(x\) are expressed in \(\mathrm{m} / \mathrm{s}^{2}\) and meters, respectively, and \(k=4 \times 10^{-4} \mathrm{m}^{3} / \mathrm{s}^{2} .\) Determine the maximum velocity and acceleration of \(B .\)

The three-dimensional motion of a particle is defined by the position vector \(r=(A t \cos t) \mathbf{i}+(A \sqrt{t^{2}+1}) \mathbf{j}+(B t \sin t) \mathbf{k}\), where \(r\) and \(t\) are expressed in feet and seconds, respectively. Show that the curve described by the particle lies on the hyperboloid \((y / A)^{2}-(x / A)^{2}-(z / B)^{2}=1 .\) For \(A=3\) and \(B=1,\) determine \((a)\) the magnitudes of the velocity and acceleration when \(t=0\), (b) the smallest nonzero value of \(t\) for which the position vector and the velocity are perpendicular to each other.

The motion of a vibrating particle is defined by the position vector \(\mathbf{r}=10\left(1-e^{-3 t}\right) \mathbf{i}+\left(4 e^{-2 t} \sin 15 t\right) \mathbf{j}\), where \(\mathbf{r}\) and \(t\) are expressed in millimeters and seconds, respectively. Determine the velocity and acceleration when \((a) t=0,(b) t=0.5 \mathrm{s}\).

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