### Critical Thinking Items

### 2.1 Relative Motion, Distance, and Displacement

- Each captain would describe other boatâ€™s motion the same because motion is independent of reference frame.
- Each captain will describe other boatâ€™s motion as moving in the backward direction because they are in their own reference frames.
- Each captain would describe the boats as moving differently because motion is a relative term.
- Each captain would describe the other boatâ€™s motion perpendicularly because they will perceive them as moving opposite to each other.

- Passenger B sees that the ball has vertical, but no horizontal, motion. Observer C sees the ball has vertical as well as horizontal motion.
- Passenger B sees the ball has vertical as well as horizontal motion. Observer C sees the ball has the vertical, but no horizontal, motion.
- Passenger B sees the ball has horizontal but no vertical motion. Observer C sees the ball has vertical as well as horizontal motion.
- Passenger B sees the ball has vertical as well as horizontal motion. Observer C sees the ball has horizontalbut no vertical motion.

### 2.2 Speed and Velocity

- No, it reflects speed but not the direction.
- No, it reflects the average speed of the car.
- Yes, it sometimes reflects instantaneous velocity of the car.
- Yes, it always reflects the instantaneous velocity of the car.

Terri, Aaron, and Jamal all walked along straight paths. Terri walked 3.95 km north in 48 min. Aaron walked 2.65 km west in 31 min. Jamal walked 6.50 km south in 81 min. Which of the following correctly ranks the three boys in order from lowest to highest average speed?

- Jamal, Terri, Aaron
- Jamal, Aaron, Terri
- Terri, Jamal, Aaron
- Aaron, Terri, Jamal

*v*

_{avg,R}and she walks for half of Loganâ€™s time, what is Loganâ€™s velocity

*v*

_{avg,L}if he walks three times as far?

- ${v}_{\text{avg,L}}=\frac{3}{2}{v}_{\text{avg,R}}$
- ${v}_{\text{avg,L}}=\frac{2}{3}{v}_{\text{avg,R}}$
- ${v}_{\text{avg,L}}=\sqrt{3{v}_{\text{avg,R}}}$
- ${v}_{\text{avg,L}}=3{v}_{\text{avg,R}}^{2}$

### 2.3 Position vs. Time Graphs

Explain how you can use the graph of position vs. time to describe the change in velocity over time.

Identify the time (*t _{a}*,

*t*,

_{b}*t*,

_{c}*t*, or

_{d}*t*) at which at which the instantaneous velocity is greatest, the time at which it is zero, and the time at which it is negative.

_{e}### 2.4 Velocity vs. Time Graphs

Identify the time, or times, at which the instantaneous velocity is greatest, and the time, or times, at which it is negative. A sketch of velocity vs. time derived from the figure will aid in arriving at the correct answers.

- The instantaneous velocity is greatest at
*f*, and it is negative at*d*,*h*,*I*,*j*, and*k*. - The instantaneous velocity is greatest at
*e*, and it is negative at*a*,*b*, and*f*. - The instantaneous velocity is greatest at
*f*, and it is negative at*d*,*h*,*I*,*j*, and*k* - The instantaneous velocity is greatest at
*d*, and it is negative at*a*,*b*, and*f*.