A particle has initial velocity 3i + 4j and acceleration of 0.4i + 0.3j. what is its speed after 10 seconds? I know the correct way to solve this question is by dealing with x and y components separately and it gets us to the answer 7√2. But what if we first find the magnitude of velocity and acceleration and then use v=u+at to find speed. This gets us to the answer 10. I know that we deal with x and y components of any vector separately but when we are just dealing with magnitude of vector, the second method should as well be right. Why are the answers different and where am I wrong?