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?
In general it is not possible to answer this question without knowing the form of the deceleration curve.
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.
I believe it is reasonable to assume average acceleration.
First you need to determine the average acceleration .
Second you need to determine the velocity at
Solution: Rearrange the equation to isolate