Question

13 the graph shows the motion of a student walking at different speeds.
student’s motion
graph: velocity (m/sec) on y - axis, time (sec) on x - axis (0 to 15), grid lines. velocity starts at 1 m/sec, stays constant until ~2 sec, increases to ~1.75 m/sec by 4 sec, stays constant until 8 sec, then decreases to 0 by 12 sec.
during which time interval does the student walk with a negative acceleration?
a 0–2 seconds
b 2–4 seconds
c 4–8 seconds
d 8–12 seconds

Explanation:

Step1: Understand Acceleration from Graph

Acceleration is the rate of change of velocity. On a velocity - time graph, the slope of the graph represents acceleration. A negative slope (where velocity is decreasing as time increases) means negative acceleration.

Step2: Analyze Each Interval

• Option A (0 - 2 seconds): The velocity is constant (slope = 0), so acceleration is 0.
• Option B (2 - 4 seconds): The velocity is increasing (positive slope), so acceleration is positive.
• Option C (4 - 8 seconds): The velocity is constant (slope = 0), so acceleration is 0.
• Option D (8 - 12 seconds): The velocity is decreasing (negative slope), so acceleration is negative.

Answer:

D. 8 - 12 seconds