Asked by anonymous

Consider a rocket in space that ejects burned fuel at a speed of vex= 2.0 km/s with respect to the rocket. The rocket burns 10 % of its mass in 340 s (assume the burn rate is constant).

(a) What is the speed v of the rocket after a burn time of 170.0 s? (suppose that the rocket starts at rest; and enter your answer in m/s)

v=

unanswered
(b) What is the instantaneous acceleration a of the rocket at time 170.0 s after the start of the engines?(in m/s2)

a=

Relevant equation: v_f = -v_ex*ln(m_final/m_initial) - g*burn time

What I tried to do: I plugged in the data, getting -2000*ln(0.95) - g*170, but got the velocity wrong. I have no idea where I went wrong, and I am stuck here, along with finding the acceleration. Can someone please help me get unstuck here. Thanks and sorry to be a bother.



Answered by Batman
notice that the rocket described in the problem is *not* under any gravitational interaction. So really the only problem with your equation is the "-g*burn time" part.

the equation you want to solve is just

v_f = -v_ex*ln(m_final/m_initial)

Answered by Phy
How to calculate M initial and M final?
Answered by Anonymous
M_final is 0.95*M_initial
Answered by juanpro
0.90Minitial?
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