Verified answer

Sketching a speed-time graph is the easiest way to solve this question.

You would have a right-angle triangle, starting from u (unknown initial speed) to zero speed and time t (also unknown).

Using v = u + at

0 = u + (-10) t

so u = 10t

Area of triangle = distance travelled

60 = 1/2 X t X 10t

therefore t = 3.46 s

So the initial speed of the car is 10(3.46) = 34.6 m/s (ans)