Question

A car is traveling at 20 meters/second and is brought to rest by applying brakes over a period of 4 seconds. What is its average acceleration over this time interval? A. It has no acceleration. B. Its acceleration is 20 meters/second2. C. Its acceleration is -5 meters/second2. D. Its acceleration is 5 meters.

Answer 1

Answer: The correct answer is C.

Explanation:

If it comes to a complete stop over a period of four seconds, that means it's velocity is going down by 5 m/s every second, as 20/4 = 5. At 1 second, the velocity is 15 m/s, then at 2 seconds, it is 10 m/s, and then at 3 seconds, it is 5 m/s, until it finally reaches 4 seconds, and is at a complete stop. Since the acceleration is bringing the velocity down rather than up, it is negative. Hope this helped :-)

Answer 2

C

Explanation:

Because every second it slows by -20/4 or -5 meters per second squared, the answer is C.