A pick up truck travelling at constant speed begins to accelerate at 1.5m/s squared for 6 seconds, by which times it has reached a speed of 20m/s. What was its original speed?

To determine the truck's original speed, we need to understand the relationship between acceleration, time, and final velocity. The formula that relates these variables is:

v = u + at

Where:
v = final velocity
u = initial velocity (original speed)
a = acceleration
t = time

Given the information in the question, we can identify the following values:
v = 20 m/s (final velocity)
a = 1.5 m/s² (acceleration)
t = 6 s (time)

Now, rearranging the formula to solve for u (initial velocity), we have:

u = v - at

Plugging in the known values:

u = 20 m/s - (1.5 m/s² * 6 s)
u = 20 m/s - 9 m/s
u = 11 m/s

Therefore, the original speed of the pick-up truck was 11 m/s.