Hello!
The velocity function is:

a) 2.3 s earlier, we can make
t = -2.3 s, in relation to our initial time:

b) Now we can make
t = 2.3 s:
Answer: 
Explanation:
According to the conservation of linear momentum principle, the initial momentum
(before the collision) must be equal to the final momentum
(after the collision):
(1)
In addition, the initial momentum is:
(2)
Where:
is the mass of the comet
is the mass of the asteroid
is the velocity of the comet, which is positive
is the velocity of the asteroid, since it is at rest
And the final momentum is:
(3)
Where:
is the final velocity
Then :
(4)
Isolating
:
(5)

Finally:
This is the final velocity, which is also in the positive direction.
Well its C, cant show you the work its in my head sorry.
Answer:
Reduce you're speed, and let the other vehicle pass you
To bring something to a stop the same force that was applied to speed it up can be used to stop it. If a greater force is used it will stop quicker.