Rocket Problem -- Solve using the Rocket Equation

  • #1
mannerplay
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Homework Statement:
Halliday Principles of Physics 10th edition
The mass of the rocket is 50 kg, the mass of the fuel is 450 kg
the rocket's maximum v rel=2 km/s
if R=10kg/s, what velocity does the rocket moves when it consumes all its fuel?
solve when the acceleration of the rocket is 20 m/s^2
Relevant Equations:
Ma=-Rv (R is the ratio which a rocket's loss of its mass and v is the relative speed of the fuel to the rocket)
I tried the second rocket equation

vf = vi + v rel * ln(Mi/Mf)

but it gives out approximately 4900 m/s for the answer
but the answer is 4160 m/s
 
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Answers and Replies

  • #2
jbriggs444
Science Advisor
Homework Helper
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What are ##v_i##, ##v_\text{rel}##, ##M_i## and ##M_f##?

You claim to have put them into the equation: ##v_f=v_i + v_\text{rel} \times ln(\frac{M_i}{M_f})## but I cannot tell what inputs you used to that equation.

If I reverse-engineer the supposedly correct answer, I come up with a different problem where the mass of the fuel is only 350 kg.

I have not been able to reverse-engineer your answer to see what you did. That is why it is important to show your work.
 

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