Question

Select the correct answer.

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 ou
this time interval?
A.
It has no acceleration.
B.
its acceleration is 20 meters/second?
C.
its acceleration is -5 meters/second-
D.
Its acceleration is 5 meters.
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Answer 1

Hi,

By definition, formula for acceleration a is:

`a=(Final\ speed - initial\ speed)/(Time)=(0\ m/s-20\ m/s)/(4\ s)=(-20\ m/s)/(4\ s)=-5\ m/s^2.`

Final speed is 0 m/s, because the car will be at rest and the end of the period of 4 seconds.

So, correct answer is C.

Be careful, correct unit of measurement for acceleration is not meters/second (as you wrote), it is meter/second², or m/s².

Have you understood ?

Green eyes.