A car is travelling at 25m/s. The driver takes his foot off the accelerator and slows down. His decceleration is two metres per second squared. How long does it take him to reach speed of fifteen metres per second squared?

V = Vo + a*t = 15 m/s, Vo = 25 m/s, a = -2 m/s^2, t = ?.

To determine how long it takes for the car to reach a speed of 15 m/s, we can use the formula:

v = u + at

where:
v = final velocity (15 m/s)
u = initial velocity (25 m/s)
a = acceleration/deceleration (-2 m/s²)
t = time

We need to rearrange the equation to solve for time (t):

t = (v - u) / a

Plugging in the given values:

t = (15 - 25) / -2
t = -10 / -2
t = 5 seconds

Therefore, it will take the car 5 seconds to reach a speed of 15 m/s when decelerating at a rate of 2 m/s².