Vectors and average acceleration

2011 AIPMT-PRE 1 question

1. 1 Motion in a Plane
   A body is moving with velocity 30 m/s towards east. After 10 seconds its velocity becomes 40 m/s towards north. The average acceleration of the body is
   A 5 m/$s^2$ B 1 m/$s^2$ C 7 m/$s^2$ D $\sqrt{7}$ m/$s^2$
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