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:

Answer:

Explanation:
We are given that
Initial velocity=u=18ft/s
Final velocity,v=38ft/s
Time=t=3 s
We have to find the average acceleration over that 3 s period.
We know that
Average acceleration,a=
Using the formula
Average acceleration,a=
Average acceleration,a=
Average acceleration,a=
Hence, the average acceleration=
The bus and the truck have the same velocity.
Also, Valerie and Owen have the same velocity.
Explanation:
It is given that,
Diameter of the semicircle, d = 45 m
Radius of the semicircle, r = 22.5 m
Speed of greyhound, v = 15 m/s
The greyhound is moving under the action of centripetal acceleration. Its formula is given by :



We know that, 


Hence, this is the required solution.