Question

A car traveling at 28 m/s starts to decelerate steadily. It comes to a complete stop in 7 seconds. What is its acceleration?

Answer 1

The car's acceleration can be modeled by the following formula:

$a = \frac{v_f - v_i}{t}$

vf represents the final velocity of the car. vi represents the initial velocity of the car. t represents the total time it took for the car to get from its initial to its final velocity.

We already have our values for our velocities and time. Plug them into the equation:

$\text{Initial velocity: 28 m/s}^{2}$
$\text{Final velocity: 0 m/s}^2$
$\text{Time: 7 seconds}$

$\frac{0-28}{7} = -\frac{28}{7} = \boxed{-4}$

The acceleration of the car is -4 m/s, or -4 meters per second.

Answer 2

The function that models the scenario is
v = init_v + acceleration * time

Plug the values into the equation,
0 = 28 + a * 7 => -28 = a * 7 => a = - 28/7 m/s.