Solved: When the mass m of a body is changing with time,

Chapter 1, Problem 21E

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QUESTION:

When the mass m of a body is changing with time, Newton’s second law of motion becomes

\(F=\frac{d}{d t}(m v)\),

where F is the net force acting on the body and mv is its momentum. Use (17) in Problems 21 and 22.

A small single-stage rocket is launched vertically as shown in Figure 1.3.19. Once launched, the rocket consumes its fuel, and so its total mass m(t) varies with time t > 0. If it is assumed that the positive direction is upward, air resistance is proportional to the instantaneous velocity v of the rocket, and R is the upward thrust or force generated by the propulsion system, then construct a mathematical model for the velocity v(t) of the rocket. [Hint: See (14) in Section 1.3.]

                                       

Text Transcription:

F=d/dt (mv)

Questions & Answers

QUESTION:

When the mass m of a body is changing with time, Newton’s second law of motion becomes

\(F=\frac{d}{d t}(m v)\),

where F is the net force acting on the body and mv is its momentum. Use (17) in Problems 21 and 22.

A small single-stage rocket is launched vertically as shown in Figure 1.3.19. Once launched, the rocket consumes its fuel, and so its total mass m(t) varies with time t > 0. If it is assumed that the positive direction is upward, air resistance is proportional to the instantaneous velocity v of the rocket, and R is the upward thrust or force generated by the propulsion system, then construct a mathematical model for the velocity v(t) of the rocket. [Hint: See (14) in Section 1.3.]

                                       

Text Transcription:

F=d/dt (mv)

ANSWER:

Step 1 of 3

The goal is to build a numerical model for the speed v(t) of the rocket

Accept a rocket of mass m, moving speed v.

Once propelled, the rocket devours its fuel so its aggregate mass m(t) shifts with time t >0.

In the event that the mass m of body is changing with time at that point Newton's second law of movement moves toward becoming,

……(i)

Here, F is the net constraint following up on the body and mv is its energy.

 

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