A landing craft of mass 12000 kg prepare itself for moon landing. when at a vertical distance 160m above the moons surface its downward velocity is 15 m/s. a retrorocket is fired to give the craft an upward thrust to slow its speed to zero as it meet the surface.calculate the needed thrust to decelerate the craft its initial downward velocity to zero as it lands.

Answer 1

This is what i did but i totally could of got it so wrong. this assignment is way harder then i thought it would be :)

Landing craft mass=12000kg
d=160m above moon surface
Vi=15m/s
g on earth=9.81m/s
g on moon g/6
g on moon=1.635m/s
Vf=0m/s
Needed thrust=??
Assuming the crafts mass doesn’t change
Assuming no interference like a moonbuggy in the way.

t=d/s
t=160m/15m/s
t=10.7seconds
a=Vf-Vi/t
a=0m/s-15m/s/10.7
a=-1.40
F=ma
12000x-1.4
=-16800N