Asprinter moving at 10 m/s slows down at a rate of 1.4 m/s2. how fast is the runner moving after 4 seconds?

vf= 4.4 m/s

Explanation:

Kinematics

Because the sprinter moves with uniformly accelerated movement we apply the following formula:

vf= v₀+at Formula (1)

Where:  

t : time in seconds (s)

v₀: initial speed in m/s  

vf: final speed in m/s  

a: acceleration in m/s²

Data

t = 4 s

v₀ = 10 m/s

a = -1.4 m/s²

Problem development

We replace data in the formula (1) to calculate the speed of the sprinter in 4 seconds :

vf = 10-1.4(4)

vf= 4.4 m/s