A car slows down from 40 m/s to 2 m/s at a constant rate of 5 m/s^2. How many seconds until the car is at 2 m/s?

Question

Physics. Help me understand what formula to use and what values are the acceleration and velocity.

Answer 1

a = acceleration = -5 m/s² [negative because the car is slowing down]

 

v_i = initial speed = 40 m/s

 

v_f = final speed = 2 m/s

 

t = length of time interval between speeds v_i and v_f

 

a = (v_f - v_i)/t

 

t = (v_f - v_i)/a = [(2 - 40) m/s] / (-5 m/s2) = 7.6 s