An object travels 23 metres in 3 seconds and then another 15 metres in 2 seconds. What is the average speed of the object in metres per second over the entire journey?

Introduction / Context:
This question illustrates the concept of average speed when an object covers different distances in different time intervals. It emphasizes that average speed must always be calculated as total distance divided by total time, not by averaging individual speeds or distances separately. The units of the final answer are also part of the test.

Given Data / Assumptions:
The object travels 23 metres in the first 3 seconds.
It travels an additional 15 metres in the next 2 seconds.
The motion is along a straight line and we treat each segment as uniform speed over that interval.
We are required to find the average speed for the full 5 second interval in metres per second.

Concept / Approach:
Average speed is defined as total distance divided by total time. We must sum the distances of all segments of motion and sum the times taken, then compute the ratio. We do not need to calculate individual speeds for each segment separately, although we could do that if desired. Units should be carefully maintained as metres and seconds to produce the final answer in m/s.

Step-by-Step Solution:
Step 1: Compute the total distance travelled.Total distance = 23 m + 15 m = 38 m.Step 2: Compute the total time taken.Total time = 3 s + 2 s = 5 s.Step 3: Use the formula average speed = total distance / total time.Average speed = 38 / 5 m/s.Step 4: Simplify 38 / 5 = 7.6.Step 5: Therefore, average speed = 7.6 m/s.

Verification / Alternative check:
We can compute the speed in each segment for understanding. In the first segment, speed1 = 23 / 3 m/s, which is approximately 7.67 m/s. In the second segment, speed2 = 15 / 2 = 7.5 m/s. The average of these numbers is about 7.585 m/s, which is close to but not exactly 7.6 m/s. The exact average speed must be 7.6 m/s from the total distance and total time calculation, so we rely on the correct formula, not the simple average of segment speeds.

Why Other Options Are Wrong:
8.0 m/s would require a total distance of 8 * 5 = 40 m, which is more than the actual 38 m travelled.
7.6 m is incorrect because it uses distance units instead of speed units and ignores the time factor.
8.0 s is only a time value, not a speed, and does not answer the question asked.
6.5 m/s does not match the ratio 38 / 5 and appears from an incorrect division or guess.

Common Pitfalls:
Some students mistakenly average the speeds of the segments rather than using total distance over total time. Others forget to include all time intervals or misread units, answering with metres or seconds instead of metres per second. Always apply the definition of average speed carefully and verify that the final unit matches what is requested.

Final Answer:
The average speed of the object over the entire motion is 7.6 m/s.