A driver entering the outskirts of a city takes her foot off the accelerator so that her car slows down from 90 km/h to 50 km/h in 10 s. Find the car's average acceleration.

Change the speeds to m/s, then divide the difference by 10 s.

The change in speed is -40 km/h, which is -11.11 m/s

The acceleration rate will be negative

To find the car's average acceleration, we can use the formula:

Average acceleration = (final velocity - initial velocity) / time

In this case, the final velocity is 50 km/h, the initial velocity is 90 km/h, and the time is 10 seconds.

Before we proceed, let's convert the velocities from km/h to m/s to match the standard units for acceleration. We know that 1 km/h is equal to 0.278 m/s.

So, the final velocity in m/s would be:

Final velocity = 50 km/h * (0.278 m/s / 1 km/h) = 13.9 m/s

The initial velocity in m/s would be:

Initial velocity = 90 km/h * (0.278 m/s / 1 km/h) = 25.0 m/s

Now, let's substitute these values into the formula:

Average acceleration = (13.9 m/s - 25.0 m/s) / 10 s

Simplifying the equation further:

Average acceleration = (-11.1 m/s) / 10 s

Therefore, the car's average acceleration is -1.11 m/s².

The negative sign indicates that the acceleration is in the opposite direction to the motion, which means the car is slowing down.