A landing craft is attempting to land on an unexplored planet in a distant solar system. As it nears the plane

Question

A landing craft is attempting to land on an unexplored planet in a distant solar system. As it nears the planet's surface, slowing down at a rate of 3.21 m/s2, its rocket engines provide an upward thrust force of 87.4 kN (kilonewtons). The craft's mass is 4480 kg. Calculate
(a) the local free-fall acceleration rate (g)
(b) the engine thrust that would be necessary for the craft to descend at a constant speed

Answer 1

do your own homework

Answer 2

F = m a
87400 N = 4480 kg a
Therefore "a" is 19.5089 m/s^2
Since the rate of slow down is established at 3.21 m/s^2, then 3.21 is what if left after removing the acceleration due to gravity; which is thus 19.5089 - 3.21 = 16.2989 m/s^2

If this acceleration due to gravity was to be exactly balanced by the thrust, then the speed of descent would be constant (assuming no atmospheric drag).
This means:
F = 4480 * 16.2989 = 73019 N

The thrust required for a constant speed descent is thus 73.019 kN.

Answer 3

The craft is slowly deacclerating at a constant rate, with use of rocket thrust. If the thrust was not there, it would acclerate at the amount of the planet's gravity. So..............
F= m*a
87.4 kN = 4.48 Tonne * a
a = 87.4/4.48 = 19 m/sec^2 appx
This counteracts the planet's gravity + allows for deaccleration. So..............
(a) Free fall rate = 19 m/sec^2-3.21 m/sec^2 = 15.8 m/sec^2 appx
(b) Constant velocity upwards thrust rate
4.48 Tonne * 15.8 m/sec^2 = 70 kN appx.

Answer 4

doesn't the gravitational pull of the planet they are landing on have any part in this equation?

Answer 5

who cares

Answer 6

====> ?

Answer 7

"Beam me up Scottie"???