Question

# The velocity of an object at $$t=0$$ is $${ \overrightarrow { v } }_{ 0 }=-4\hat { j } m/s$$. It moves in a plane with constant acceleration $$\overrightarrow { a } =\left( 3\hat { i } +8\hat { j } \right) m/{ s }^{ 2 }$$. What is its velocity after $$1s$$

A
6
B
5
C
7
D
8

Solution

## The correct option is B 5using equation of motion.$$V = u + at$$Now write the equation of motion in vector form$$a = \left( {3i + 8j} \right)m/{s^2}$$$$v = - 4j + \left( {3i + 8j} \right)1$$As$$u = - 4jm/s\,\,and\,\,t = 1\sec$$Or$$v = 3i + 4j$$The final velocity $$= {\left( {{3^2} + {4^2}} \right)^{\frac{1}{2}}} = 5m/s$$Hence, the final velocity is $$5m/s$$ Physics

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