physics question multiple choice

Question

an object traveling in a straight line with v=-15[m/s], and a=+2 [m/s^2] this object is:

a) traveling at a constant speed towards the origin.

b) moving away from the origin speeding up

c) none of the above

d) moving away from origin slowing down

Answer 1

Keep in mind that the signs on the velocity and acceleration vectors, refer to the directions of the vectors. If the velocity and acceleration vectors are in the same direction, then the object is speeding up, while moving in the direction of the velocity. If the velocity and acceleration vectors are in opposite directions, then the object is slowing down, while moving in the direction of the velocity.

For example:

If an object has a positive velocity, and a positive acceleration, then it is moving in the positive direction, and speeding up.

If an object has a positive velocity, and a negative acceleration, then it is moving in the positive direction, and slowing down.

If an object has a negative velocity, and a negative acceleration, then it is moving in the negative direction, and speeding up.

If an object has a negative velocity, and a positive acceleration, then it is moving in the negative direction, and slowing down.

In this question, the velocity is -15 m/s, and the acceleration is +2 m/s², so the object is moving in the negative direction, and slowing down. Assuming that it started at the origin, it is moving away from origin and slowing down.

Answer 2

Because the object is moving with an initial velocity and a positive acceleration, the object must be speeding up in the direction away from the origin.

A) is incorrect, because when an object has a constant velocity, there is no acceleration.

B) CORRECT ANSWER

C) Incorrect answer

D) an object that is slowing down, has a negative acceleration.