My car is accelerating at a rate of 4.0 km/hr/s. The original velocity
was 85 km/hr south. What will the velocity be in 40 seconds?

245 km/h south

Explanation:

Since the motion of the car is a uniformly accelerated motion (=constant acceleration), we can use the following suvat equation:

where

u is the initial velocity

a is the acceleration

t is the time

v is the final velocity

For the car in this problem we have:

is the initial velocity (taking south as positive direction)

is the acceleration (the direction is not specified; I assume it is south, so it is also positive)

t = 40 s is the time elapsed

Therefore, the final velocity is

And since the value is positive, the direction is south.

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