Question

a partical moving towards east with 30 m/s turn to towards north with 40 m/s. find the magnitude and direction of change of velocity.

Answer 1

Suddenly'word in the question should not be there.

If velocity changes suddenly then time period can not be taken as 10s.

So, here, the questioner should mention that with uniform acceleration ,the velocity changes from initial 5 m/s due east to final 5m/s due north in 10s.

In this context the other two answers should mention that acceleration being uniform we can use the formula, a=[v( final)-v( initial)]/time.

Both the answers are good and I am sure both authors had uniform acceleration in their minds.