# A car starts from rest at a stop light and reaches 20 m/s in 3.5 s. Determine the acceleration of the car.

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### 1 Answer

The acceleration is a characteristic of the variable motions; that is, where the speed is not constant. The acceleration of a movement is the rate with which the speed varies, per unit of time.

When the speed varies uniformly, the acceleration of the movement is calculated by the following equation:

a = Δv/Δt = (v – v0)/(t – t0)

Where:

Δv = v – v0, is the difference between the final speed and the initial speed, in the time interval considered.

Δt = t – t0, is the time interval.

In our problem we have:

v0 = 0; v = 20 m/s; t0 = 0; t = 3.5 s

Substituting in the equation:

a = (20 – 0)/3.5 – 0)

a = 5.71 m/s^2

**So the car has an acceleration of 5.71 m/s^2**