PROBLEM

A paperboy rode his bike at 3 m/s. After being chased by a dog for 8 seconds, he was traveling at a speed of 6 m/s.

QUESTION: What is his acceleration?

• The acceleration is 0.375 m/s².

QUESTION: Was he speeding up or slowing down?

• The paperboy is speeding up since the final velocity is greater than the initial velocity and the resulting acceleration is a positive number.

SOLUTION AND EXPLANATION:

For Question #1,

Given:

• initial velocity = 3 m/s
• final velocity = 6 m/s
• time elapsed = 8 s

» Find the acceleration of the object.

Therefore, the bike is accelerating at 0.375 m/s².

For Question #2,

When an object is speeding up, we can say that its velocity increases over time. So the resulting acceleration has a positive value. Also judging from the final and initial velocities, the final velocity has a greater value so the change in velocity (final velocity minus the initial velocity) is a positive number.

In the case where an object is slowing down, it's the opposite. The initial velocity has a greater value so the change in velocity is a negative number. Thus, the resulting acceleration is negative. We can therefore say that the object's velocity decreases over time.

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