State the rule for integration by parts. In practice, how do you use it?
Read more
Table of Contents
Textbook Solutions for Calculus: Early Transcendentals
Question
A rocket is fired straight up, burning fuel at the constant rate of \(b\) kilograms per second. Let \(v=v(t)\) be the velocity of the rocket at time \(t\) and suppose that the velocity \(u\) of the exhaust gas is constant. Let \(M=M(t)\) be the mass of the rocket at time \(t\) and note that \(M\) decreases as the fuel burns. If we neglect air resistance, it follows from Newton's Second Law that
\(F=M \frac{d v}{d t}-u b\)
where the force \(F=-M g\). Thus
Let \(M_{1}\) be the mass of the rocket without fuel, \(M_{2}\) the initial mass of the fuel, and \(M_{0}=M_{1}+M_{2}\). Then, until the fuel runs out at time \(t=M_{2} / b\), the mass is \(M=M_{0}-b t\).
(a) Substitute \(M=M_{0}-b t\) into Equation 1 and solve the resulting equation for \(v\). Use the initial condition \(v(0)=0\) to evaluate the constant.
(b) Determine the velocity of the rocket at time \(t=M_{2} / b\). This is called the burnout velocity.
(c) Determine the height of the rocket \(y=y(t)\) at the burnout time.
(d) Find the height of the rocket at any time \(t\).
Solution
The first step in solving 7 problem number trying to solve the problem we have to refer to the textbook question: A rocket is fired straight up, burning fuel at the constant rate of \(b\) kilograms per second. Let \(v=v(t)\) be the velocity of the rocket at time \(t\) and suppose that the velocity \(u\) of the exhaust gas is constant. Let \(M=M(t)\) be the mass of the rocket at time \(t\) and note that \(M\) decreases as the fuel burns. If we neglect air resistance, it follows from Newton's Second Law that \(F=M \frac{d v}{d t}-u b\)where the force \(F=-M g\). ThusLet \(M_{1}\) be the mass of the rocket without fuel, \(M_{2}\) the initial mass of the fuel, and \(M_{0}=M_{1}+M_{2}\). Then, until the fuel runs out at time \(t=M_{2} / b\), the mass is \(M=M_{0}-b t\).(a) Substitute \(M=M_{0}-b t\) into Equation 1 and solve the resulting equation for \(v\). Use the initial condition \(v(0)=0\) to evaluate the constant.(b) Determine the velocity of the rocket at time \(t=M_{2} / b\). This is called the burnout velocity.(c) Determine the height of the rocket \(y=y(t)\) at the burnout time.(d) Find the height of the rocket at any time \(t\).
From the textbook chapter Techniques of Integration you will find a few key concepts needed to solve this.
Visible to paid subscribers only
Step 3 of 7)Visible to paid subscribers only
full solution