A car of mass 1,000 kilograms is moving initially at the speed of 22 meters/second. When the brakes are applied, it takes the car 3.0 seconds to stop. What is the force required to stop the car?

To find the force required to stop the car, we can use Newton's second law of motion, which states that the force (F) is equal to the mass (m) of an object multiplied by its acceleration (a):

\[ F = m \cdot a \]

First, we need to calculate the acceleration. The car initially has a speed (\( v_0 \)) of 22 m/s and it comes to a stop, so the final speed (\( v_f \)) is 0 m/s. The car takes 3.0 seconds to stop (\( t \)).

We can find the acceleration using the formula:

\[ a = \frac{v_f - v_0}{t} \]

Substituting in the known values:

\[ a = \frac{0 \, \text{m/s} - 22 \, \text{m/s}}{3.0 \, \text{s}} \]
\[ a = \frac{-22 \, \text{m/s}}{3.0 \, \text{s}} \]
\[ a \approx -7.33 \, \text{m/s}^2 \]

Now, we can calculate the force needed to stop the car:

Given the mass (\( m \)) of the car is 1,000 kg, we plug the values into the formula for force:

\[ F = m \cdot a \]
\[ F = 1,000 \, \text{kg} \cdot (-7.33 \, \text{m/s}^2) \]
\[ F \approx -7,330 \, \text{N} \]

The negative sign indicates that the force is acting in the opposite direction of the car's motion. However, we are interested in the magnitude of the force required, which is:

\[ F \approx 7,330 \, \text{N} \]

Now, if we convert this to scientific notation, it is:

\[ F \approx 7.3 \times 10^3 \, \text{N} \]

So the correct answer is:

**C. 7.3 × 10³ newtons**