Projectiles

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May 4th 2009, 04:43 AM
djmccabie

Projectiles

A ball is kicked from point A on a horizontal field with an initial speed of 24.5 m/s at an angle of 30 degrees above the horizontal. The ball first hits the ground again at point B.

Calculate the time of flight of the ball

Ok so i have worked out

Vx = 24.5cos30 = 21.218
Vy = 24.5sin30 - 9.8t = 12.25

now i'm assuming i have to do something with these numbers but I have no idea :S
May 4th 2009, 05:15 AM
skeeter

Quote:

Originally Posted by djmccabie

A ball is kicked from point A on a horizontal field with an initial speed of 24.5 m/s at an angle of 30 degrees above the horizontal. The ball first hits the ground again at point B.

Calculate the time of flight of the ball

Ok so i have worked out

Vx = 24.5cos30 = 21.218
Vy = 24.5sin30 - 9.8t = 12.25

now i'm assuming i have to do something with these numbers but I have no idea :S

$\Delta y = v_0 \sin{\theta} \cdot t - \frac{1}{2}gt^2$

the overall displacement in the y-direction is 0 ...

$0 = v_0 \sin{\theta} \cdot t - \frac{1}{2}gt^2$

$0 = t\left(v_0 \sin{\theta} - \frac{1}{2}gt\right)$

$v_0 \sin{\theta} - \frac{1}{2}gt = 0$

$t = \frac{2v_0 \sin{\theta}}{g}$
May 4th 2009, 05:24 AM
djmccabie

Quote:

Originally Posted by skeeter

the overall displacement in the y-direction is 0 ...

This is what I was looking for :D thankyou!

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