Answer:
The decelerating force is

Solution:
As per the question:
Frontal Area, A =

Speed of the spaceship, v =

Mass density of dust,

Now, to calculate the average decelerating force exerted by the particle:
(1)
Volume,

Thus substituting the value of volume, V in eqn (1):

where
A = Area
v = velocity
t = time
(2)

From Newton's second law of motion:

Thus differentiating w.r.t time 't':

where
= average decelerating force of the particle
Now, substituting suitable values in the above eqn:
