Posted by **Hayden** on Monday, October 20, 2008 at 6:54pm.

A ball is thrown horizontally off a 35 m tall building. It hits the ground 80 m from the bottom of the tower.

a. what is the balls time in the air

[i got 2.67]

b. what is its initial velocity?

[i got 0]

c. What is the magnitude and direction of its velocity as it strikes the ground?

Could someone please check my answers and explain how to do question c??

- Physics help again! -
**Michael**, Monday, October 20, 2008 at 7:04pm
b is wrong. should be a vector in the x dircection. will add more later

- Physics help again! -
**Damon**, Monday, October 20, 2008 at 7:22pm
Well it is thrown horizontally so its initial velocity in the vertical direction is zero. That means it just plain falls while continuing at the original horizontal velocity. So:

Time to fall 35 m

0 = 35 + 0 - 4.9 t^2

t^2 = 35/4.9

t = 2.67 seconds in the air

t went 80 meters in 2.67 seconds so initial and final and in between horizontal velocity is 80/2.67 = 30 m/s

Well we know the horizontal velocity is zero during this whole experience so we need the vertical velocity when it falls for 2.67 seconds

v = a t = - 9.8 * 2.67 = - 26.2 m/s

so when it crashes it is still going 30 ahead and is going 26.2 down

magnitude = sqrt(26.2^2 +30^2) = 39.8 m/s

tangent of angle down from horizontal = 26.2/30

so angle = 41.1 degrees

- Typos ! -
**Damon**, Monday, October 20, 2008 at 7:25pm
Well it is thrown horizontally so its initial velocity in the vertical direction is zero. That means it just plain falls while continuing at the original horizontal velocity. So:

Time to fall 35 m

0 = 35 + 0 - 4.9 t^2

t^2 = 35/4.9

t = 2.67 seconds in the air

It went 80 meters in 2.67 seconds so initial and final and in between horizontal velocity is 80/2.67 = 30 m/s

Well we know the horizontal velocity is 30 m/s during this whole experience so we need the vertical velocity when it falls for 2.67 seconds

v = a t = - 9.8 * 2.67 = - 26.2 m/s

so when it crashes it is still going 30 ahead and is going 26.2 down

magnitude = sqrt(26.2^2 +30^2) = 39.8 m/s

tangent of angle down from horizontal = 26.2/30

so angle = 41.1 degrees

- iqpmaoh gnoy -
**iqpmaoh gnoy**, Wednesday, November 19, 2008 at 9:05pm
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