Acceleration is change in velocity over change in time. Your Δv is +13.9, since you increased speed by 50 km/h which is 13.9 m/s, and your Δt is 10s. 13.9/10 = 1.39 m/s^2, the standard units for acceleration. Make sense?
The type of mixture that is formed when a solid is stirred into a liquid and dissolves is called suspension. The particles involved or being mixed in this type of mixture is large enough that can be seen by the naked eye without the aid of any device. A suspension mixture has a heterogeneous mixture.