Average Acceleration and Max Speed?

Question

A rocket sled has a ,mass of 4440 kg and is propelled by a solid-propellent rocket motor of 890,000-N thrust which burns for 3.9 sec.
a) what is the sled's average acceleration and max speed?
b) This sled has a max acceleration of 30g (30a). How can
that be considering the data given?
c) If the seld travels a distance of 1530m while attaining a top speed of 860 m/sec, what is its average acceleration? How did it attain that high a speed?

Answer 1

Initial mass Mi = 4440 kg. Max accel of 30 g implies final mass Mf = 890000/(30*g) = 3024 kg, so propellant mass = Mi-Mf =1416 kg. Specific impulse = 890000*3.9/1416 = 2451 n-s/kg = 250 kg(force)-s/kg = 250 "seconds". Exhaust velocity Vex = 2451 m/s.
a) Max (final) velocity v = Vex * ln(Mi/Mf) = 2451 * 0.3841 = 941 m/s. Average acceleration = v/t = 241.4 m/s^2 = 24.61 g.
b) The mass decreases as described above.
c) The distance and max-speed numbers given here describe a different system, either lower total impulse or different masses, as they disagree with the results above. With an unknown thrust and burn duration and time-varying mass, one cannot solve for average acceleration given distance and speed, and describe how it attained that high a speed.

Answer 2

very obscure question devoid of information .. this relies upon on numerous parameters, and preliminary circumstances.. the pliability of the band in question comes into play too. choose greater information