Question

3. The brakes of an automobile traveling with a velocity of 50 ft/s are suddenly applied. If the automobile comes to a stop after 5 s, what is its acceleration?

Answer 1

By definition, the acceleration is given as a rate of speed change:

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

where $v_f = 0ft/s$ is the finall speed (car stops), $v_i = 50ft/s$ is initial speed, and $t = 5s$ is the time. Thus, obtain:

$$a = \dfrac{0-50ft/s}{5s} = -10ft/s^2$$

Answer. $-10ft/s^2$.