Question

A train engineer started the train from a standstill and sped up to 5 m/s, she then rounded a corner at a constant speed. She then sped the train up to 10 m/s on the next straightaway. Next, the train chugged around another bend at 10 m/s, and then its speed slowed to 5 m/s after coming out of the bend. Finally, the train reached the station, and the engineer applied the brakes and brought the engine to a stop. How many times did the train accelerate?
Responses
A 2
B 4
C 5
D 6

Answer 1

To determine how many times the train accelerated, we need to analyze the different segments of motion described.

1. **Starting from a standstill to 5 m/s (Acceleration)**: The train accelerates from 0 m/s to 5 m/s.
2. **Rounding a corner at constant speed (No acceleration)**: The train maintains a speed of 5 m/s while rounding the corner.
3. **Speeding up to 10 m/s (Acceleration)**: The train accelerates from 5 m/s to 10 m/s.
4. **Chugging around another bend at constant speed (No acceleration)**: The train maintains a speed of 10 m/s while rounding this bend.
5. **Slowing to 5 m/s (Deceleration)**: The train decelerates from 10 m/s to 5 m/s.
6. **Applying brakes to come to a stop (Deceleration)**: The train decelerates from 5 m/s to 0 m/s.

Now, let's count the accelerations (including decelerations):
- 1st acceleration (0 m/s to 5 m/s)
- 2nd acceleration (5 m/s to 10 m/s)
- 3rd deceleration (10 m/s to 5 m/s)
- 4th deceleration (5 m/s to 0 m/s)

Although deceleration is often considered as negative acceleration, still we count each instance of change in speed, whether an increase or decrease, as an acceleration event.

So, the total number of accelerations (including decelerations) is **4**.

The correct answer is **B 4**.