# After what time interval does the ball strike the ground

#### 012435

1. Homework Statement
A ball is thrown downward with initial speed of 8m/s from a height of 30m.

2. Homework Equations
\After what time interval does the ball strike the ground

3. The Attempt at a Solution

acceleration will equal -9.8m/s^2 because it's free fall
would i use equation V=Vo-gt

constant speed of a horse is 10m/s. distance from limb to saddle is 3m

A) find horizontal distance between saddle and limb?
B) for what time interval is he in the air?

Attempted solution:
X=Xo+Vo(t)+V2(a)(t^2)
what equation do you use to find the time ... Yf=Yi+Vi(t)+1/2g(t^2) and rearange it to

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#### learningphysics

Homework Helper
I'm confused. There seems to be two questions... one about a ball... about about a horse and saddle?

#### 012435

sorry. it's two different problems

#### learningphysics

Homework Helper
sorry. it's two different problems
This is the right equation to use for the first problem:

Yf=Yi+Vi(t)+1/2g(t^2)

but you need to be careful about directions and signs... you've taken downwards as positive here...

#### HallsofIvy

Homework Helper
1. Homework Statement
A ball is thrown downward with initial speed of 8m/s from a height of 30m.

2. Homework Equations
\After what time interval does the ball strike the ground

3. The Attempt at a Solution

acceleration will equal -9.8m/s^2 because it's free fall
would i use equation V=Vo-gt
Since you are NOT given the time but ARE given a distance, it would be better to use a distance formula: d= (1/2)gt2+ v0t. Donht forget that v0 is negative.

constant speed of a horse is 10m/s. distance from limb to saddle is 3m

A) find horizontal distance between saddle and limb?
B) for what time interval is he in the air?

Attempted solution:
X=Xo+Vo(t)+V2(a)(t^2)
what equation do you use to find the time ... Yf=Yi+Vi(t)+1/2g(t^2) and rearange it to
This makes no sense to me at all. What does the "distance from saddle to limb" . At some paces some horses can go 10m/s while always having at least one foot on the ground- they are never "in the air".

And what "limb"? A foreleg? Or is this a limb of a tree? Did you leave something out? is the horse jumping over a limb?

#### aliaze1

Since you are NOT given the time but ARE given a distance, it would be better to use a distance formula: d= (1/2)gt2+ v0t. Donht forget that v0 is negative.
yea i would use this formula

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