Question

When an object is dropped from the top of a tall cliff, your teacher tells you to use -10 m/s2 for the approximate acceleration due to gravity. What sign should the displacement of the object have and why?
A) The displacement should be positive, because it only moves in one direction.
B) The displacement should be positive, because this choice would make calculations easier
C) The displacement should be negative, because the negative represent a downward direction.
D) The displacement should be positive, because you can never have less than zero displacement.

The truck is described as travelling at 30mph to the west. The quantity described here is a(n)
A) speed
B) velocity
C) acceleration
D) kinetic energy

Answer 1

1- C

2-B

Those are your answers hope this helps :)

Answer 2

1. Answer: Option C

Displacement is a vector quantity. It has both magnitude as well as direction. Hence, it can be positive,  zero or negative. In the given question, downward direction is taken as negative. This we have come to know from the downward acceleration $-10m/s^2$. The negative sign indicates that downward direction is considered negative.

Now, since the object is dropped from the top. The displacement should be negative, because the negative represent a downward direction.

2. Answer: velocity

The truck is travelling at 30 mph to the west. From the unit mph (miles per hour), we know its a magnitude of velocity. West indicates the direction. Hence, the given quantity is a vector -velocity.

It is not speed because speed only indicates the magnitude and not the direction. speed is a scalar quantity.