# A ball is moving with speed 20 m/s collides with a smooth surface as shown in figure. the magnitude of change in velocity of the ball will be 1) 10root3 m /s 2) 20root m/s 3) 40/root3 m/s 4) 40 m/s

Dear student,

Initial velocity, $\stackrel{\to }{v}=20\left(-\mathrm{cos}60°\stackrel{^}{i}-\mathrm{cos}30°\stackrel{^}{j}\right)$
Final velocity, $\stackrel{\to }{v}\text{'}=20\left(-\mathrm{cos}60°\stackrel{^}{i}+\mathrm{cos}30°\stackrel{^}{j}\right)$
Change in velocity = Final velocity - Initial velocity

Regards

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