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September 15, 2014

September 15, 2014

Posted by **Sejul** on Sunday, January 29, 2012 at 3:18pm.

a) What is the ball's horizontal velocity at the maximum height of the ball's trajectory?

b) What is the horizontal displacement of the ball just before it lands down field?

- Physics -
**Damon**, Sunday, January 29, 2012 at 3:28pmThere is no horizontal force on the ball.

So why would its horizontal velocity change?

It does not, until it hits the ground or is headed or kicked.

u =30 cos 30

Q : How long is it in the air?

A : Twice as long as it takes to stop moving up at the top of its trajectory

Q : How long does it take to get to the top?

A : v = Vi - g t

v = 0 at the top

but Vi = 30 sin 30 = 15 m/s

so 0 = 15 - g t

so

t = (15/9.8) seconds to the top

so time in air = 2 t = 30/9.8

Q : How far does it go down the field in (30/9.8) seconds?

A : (30/9.8) u = (30/9.8)(30 cos 30)

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