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A boy kicked a ball with …

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A boy kicked a ball with initial speed of 19.6 m/s at 45° angle. Another boy who was standing 67.4 m away starts to run to meet the ball.what must be the speed of the boy in order to catch the ball before the ball hits the ground.

  • 1 answers

Payal Singh 6 years, 11 months ago

 Intial velocity u = 19.6m/s 

angle = 45

As the football ll move like a projectile, So

Range = {tex}u^2sin2\theta \over g{/tex} = {tex}{u^2sin90^o \over g } = {u^2\over g} {/tex}={tex}{19.6\times 19.6\over 9.8} = 39.2 m{/tex}

Time of Flight = {tex}{2u sin\theta\over g} = {2 \times 19.6 \over 9.8\times \sqrt 2} = {4\over \sqrt 2}{/tex} = {tex}2\sqrt 2{/tex} s

Distacne that the another boy have to cover = 67.4 - 39.2 = 28.2m

Speed of boy = {tex}{28.2\over 2\sqrt 2} = {14.1\over 1.41} = {141\times 100\over 141\times 10} = 10m/s{/tex}

 

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