# A car driving at 41m/s hits the brakes and comes to a stop in 4.8 seconds. How fast was it going after 2.4 seconds?

##### 2 Answers

In general it is not possible to answer this question without knowing the form of the deceleration curve.

#### Explanation:

In the (extremely unlikely) case that deceleration is linear, the car would have been going 20.5 m/s after 2.4 sec.

The image below shows 3 possible (of infinitely many) deceleration patterns with different speeds for each one at time 2.4 seconds.

#### Explanation:

I believe it is reasonable to assume average acceleration.

**First** you need to determine the **average acceleration** .

**Known:**

initial velocity,

final velocity,

time interval,

**Unknown:**

acceleration,

**Equation:**

**Solution:**

**Second** you need to determine the velocity at

**Known:**

acceleration,

beginning velocity,

time interval,

**Unknown:**

velocity at

**Equation:**

**Solution:** Rearrange the equation to isolate