Assuming motion is on a straight path, the result of two positive components of a vector would also be a positive value since both are having positive signs and directions. The direction would be the same with the motion as well. Hope this answers the question. Have a nice day.
Because the act of braking is an example of negative acceleration.
Example: if the rate of braking was say 2 meters per second^2, and the starting velocity was 10 m/s, it would take 5 seconds to come to a stop(during those 5 seconds you would still be moving).
Answer:
(a) 
(b) 
(c) 
Explanation:
(a) According to Newton's second law, the acceleration of a body is directly proportional to the force exerted on it and inversely proportional to it's mass.

(b) According to Newton's third law, the force that the sled exerts on the girl is equal in magnitude but opposite in the direction of the force that the girl exerts on the sled:

(c) Using the kinematics equation:

For the girl, we have
and
. So:

For the sled, we have
. So:

When they meet, the final positions are the same. So, equaling (1) and (2) and solving for t:

Now, we solve (1) for 

Question 2 is because the passengers have inertia, which is a tendency to resist change in motion
The answer should be D) Cold air because even though its true sound can travel through all types of matter, air which is a gas, can travel but it travels SLOWLY while sound travels quickly in SOLIDS.