SOLUTIONS TO EXERCISE 21

The astronaut started moving with a momentum p = mv = 95 * 3.5 newtons.
She ended her motion with a momentum 95 * 0.5 newtons in the opposite direction,
or (95 * (-0.5)) newtons in the original direction.

(a) The total change in momentum was thus the starting minus the ending momentum,
or (95 * 3.5) - (95 * (-0.5) = 95 * 4 = 380 newtons.

(b) For the thruster rocket to produce 380 newtons, it had to fire for

   380 N
  -------- = 8.4 seconds.
   45 N/s

(c) Since F = ma, the acceleration a = F/m.  So during that time, the astronaut's 
acceleration was  (45 N) / (95 kg) = 0.47 m/s2.