a 8.0 * 104 kg spaceship is at rest in deep space. it's thrusters provide a force of 1200 kn. the spaceship fires its thrusters for 20 s, then coasts for 12 km. how long does it take the spaceship to coast this distance?

40 seconds

Explanation:

Thrusting speed = V

Where V=at

a = F/m

Therefore V = Ft/m

F = 1200kN = 1200000N

t = 20s

m = 8.0 * 104 kg

V = 1200000 * 20 / 80000

V = 300m/s

Time for the spaceship to coast a distance of 12km

Distance = Vt

t = 12000/300 = 40seconds