What is the car's average acceleration?

Question

A car accelerates from 23m/s to 7m/s in 4 seconds. What is the car's average acceleration?

 

Multiple Choice:

A) -4m/s^2

B) 5.75 m/s^2

C) 1.75m/s^2

D) 4 m/s^2

 

I know the answer is A) -4m/s^2. But, why? SHOW WORK

Answer 1

Acceleration is change in velocity over time. In equations, that looks like:

 

a= Δv/t= (v_f-v_i)/t

 

Where v_i is initial velocity and v_f is final velocity. Plugging in the numbers we get:

 

a=(7-23)/4= (-16)/4= -4 m/s²

 

Answer 2

The end speed is 7 m/s^2, start speed is 23 m/s^2.

 

Think of it as a simple averaging problem: (7-23)/2 = -16/2 = -4

 

You can more or less ignore the m/s^2 to do the math because the units are all the same.