Go Back   Physics Help Forum > College/University Physics Help > General Physics

General Physics General Physics Help Forum

LinkBack Thread Tools Display Modes
Old Jan 8th 2018, 03:30 PM   #1
Senior Member
Join Date: Nov 2013
Location: New Zealand
Posts: 534
Sticky rocket problem

I'm trying to get my head around problem 3.10 from John R. Taylor's book on Classical Mechanics:

3.10 * Consider a rocket (initial mass $\displaystyle m_o$) accelerating from rest in free space. At first, as it speeds up,
its momentum p increases, but as its mass m decreases p eventually begins to decrease. For what value of m is p maximum?
Earlier in the book he gives these three equations and which appear to be the only pertinent ones:
  • (3.4) $\displaystyle dP = m \: dv + dm \: v_{ex} = F_{ext} dt$
  • (3.5, 3.7) $\displaystyle m \dot{v} = -\dot{m}v_{ex}$
  • (3.8) $\displaystyle v-v_0 = -v_{ex} \: ln(\frac{m}{m_0})$

(3.4, 3.5, 3.7, 3.8) are the reference numbers of those equations in the book.

where m0 is the initial mass of the rocket (including the mass of fuel) and Vex is the velocity of the propellant coming out of the rocket. dm is the mass of the propellant exiting the rocket and v is the forward velocity of the rocket with v0 being the initial velocity at time t = 0.

The question seems to be asking for momentum (p) purely in terms of mass (m) and constants. However my attempts always seem to end up with a velocity (v) term or time (t) term and according to the text book this is supposed to be an easy problem. Any suggestions?
Burn those raisin muffins. Burn 'em all I say.
kiwiheretic is offline   Reply With Quote

  Physics Help Forum > College/University Physics Help > General Physics

problem, rocket, sticky

Thread Tools
Display Modes

Similar Physics Forum Discussions
Thread Thread Starter Forum Replies Last Post
Ion Propulsion Rocket Momentum arcana Equilibrium and Elasticity 1 Mar 25th 2016 05:00 AM
Windowless rocket problem is NO PROBLEM !!! tesla2 Advanced Optics 0 Dec 22nd 2012 04:32 AM
Dymanics-how long was the rocket in the air? cherry_t Kinematics and Dynamics 2 Apr 8th 2010 11:19 PM
Rocket Problem link88 Kinematics and Dynamics 3 Jan 8th 2010 04:49 AM
Rocket above Earth Question jello17 Kinematics and Dynamics 1 Jan 21st 2009 07:15 PM

Facebook Twitter Google+ RSS Feed