What was the initial speed of a car if its speed is 40 m/s after 5 seconds of accelerating at 4 m/s27
A. 10 m/s
B. 60 m/s
C. 20 m/s
D. 25 m/s
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Explanation:

We are asked to find the initial speed of a car.

We are given the final speed, the time, and the acceleration, so we will use the following kinematic equation:

We know the final speed is 40 meters per second, the acceleration is 4 meters per second squared, and the time is 5 seconds.

Substitute the values into the formula.

Multiply inside the parentheses.

We are solving for the initial speed, so we must isolate the variable .  

20 meters per second is being added to . The inverse operation of addition is subtraction. Subtract 20 m/s from both sides of the equation.

The initial speed of the car is 20 meters per second and choice C is correct.

+15-35=-20

going in opposite directions