A football is kicked with a velocity of 20 m/s at an angle of $45^{\circ}$ with the horizontal. Find the time taken by the ball (in sec) to strike the ground. Give answer correct to 1 decimal place
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Solution

Take the origin at the point where the ball is kicked, vertically upward as the y-axis and the horizontal in the plane of motion as the x-axis. The initial velocity has the components:
$u_{x} = (20 m / s) c o s 45^{\circ} = 10 \sqrt{2} m / s a n d u_{y} = (20 m / s) s i n 45^{\circ} = 10 \sqrt{2} m / s . W h e n t h e b a l l r e a c h e s t h e g r o u n d, y = 0. u s i n g y = u_{y} t - \frac{1}{2} g t^{2}, 0 = (10 \sqrt{2} m / s) t - \frac{1}{2} \times (10 m / s^{2}) \times t^{2} O r, t = 2 \sqrt{2} s = 2.8 s .$

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