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**final velocity...need help!!**

## Homework Statement

An object is to be thrown through a window 3.25 m high a distance 8 m away. It is launched at an angle 75 degree above the horizontal.

The initial launch speed at the specified angle which will allow the projectile to pass through the window is 13.3 m/s.

What is the final speed of the object (that is, the speed at which it flies through the window)?

Y= height

Yo= initial height

Voy= initial speed

Vf= final velocity

g= gravity

t= time

## Homework Equations

1)Y= Yo+Voy*t-(1/2)gt^2

2)Vf= Vo+at

**3. The Attempt at a Solution**

By using the y= yo+Voy*t-(1/2)gt^2 formula,

= 3.25+ (13.3sin75)t-(1/2)(-9.81)t^2

I found the time t=2.85 s

But then the answer i got by using the formula Vf= Vo+at

= 13.3+ (-9.81)(2.85)

= -14.7 m/s

IS wrong!!What is my mistake??

By using the y= yo+Voy*t-(1/2)gt^2 formula,

= 3.25+ (13.3sin75)t-(1/2)(-9.81)t^2

I found the time t=2.85 s

But then the answer i got by using the formula Vf= Vo+at

= 13.3+ (-9.81)(2.85)

= -14.7 m/s

IS wrong!!What is my mistake??