A spaceship is pulled toward the ground by gravity. Offsetting this force, the ship fires a rocket directly downward, consuming fuel at a rate of pounds per second and the exhaust material has a constant speed of feet per second relative to the rocket. Find a formula giving the distance the spaceship falls in time if it is at rest at time and has initial weight of pounds.

The motion of the rocket is governed by the equation

We are given

So,

Then, since we have . Therefore,

And so,

Then since we have

Hence, the equation of motion is

The answer looks wrong in Apostol- the -ct element is supposed to be -cw/k. It would only be -ct if the position when the fuel runs out was requested, T=W/k.

My bad *again*… I wasn’t subtracting the constant.