Question

which of the following describes constant velocity?

a. your puppy is running in circles around a large, circular table.
b. a boy riding a bicycle hits the brakes and stops suddenly.
c. your mom drives 60 miles per hour on the freeway.
d. a kite flies up into the sky and then starts falling down again.

Explanation:

Define constant velocity

Using the Kinematics Definitions knowledge point

$$ \vec{v} = \text{constant} \iff \text{speed } |\vec{v}| = \text{constant} \text{ and direction of motion is unchanged (straight line)} $$

Analyze option A

Using the Kinematics Definitions knowledge point

$$ \text{Running in circles} \implies \text{direction changes continuously} \implies \vec{v} e \text{constant} $$

Analyze option B

Using the Kinematics Definitions knowledge point

$$ \text{Hitting brakes and stopping} \implies \text{speed decreases to zero} \implies \vec{v} e \text{constant} $$

Analyze option C

Using the Kinematics Definitions knowledge point

$$ \text{Driving } 60\text{ mph on a straight freeway} \implies \text{constant speed and constant direction} \implies \vec{v} = \text{constant} $$

Analyze option D

Using the Kinematics Definitions knowledge point

$$ \text{Flying up and falling down} \implies \text{direction reverses and speed changes} \implies \vec{v} e \text{constant} $$

Answer:

• (A) Your puppy is running in circles around a large, circular table.
• (B) A boy riding a bicycle hits the brakes and stops suddenly.
• (C) Your mom drives 60 miles per hour on the freeway. (Correct answer)
• (D) A kite flies up into the sky and then starts falling down again.