Question

A car slows from 22 m/s to 3.0 m/s with a constant acceleration of -2.1 m/s2.  How long does it require in the unit of seconds?

Answer 1

By definition, the acceleration is given as follows:

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

where $v_f = 3m/s,v_i = 22m/s$ are final and initial speeds respectively, and $t$ is the time. Expressing the time and substituting $a = -2.1m/s^2$, obtain:

$$t = \dfrac{v_f-v_i}{a} = \dfrac{3m/s - 22m/s}{-2.1m/s^2} \approx 9.0s$$

Answer. 9.0 s.