- #1

luvsk8ing

- 10

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## Homework Statement

There is a link to the problem and its picture here: http://media.wiley.com/product_data/excerpt/19/04717580/0471758019-1.pdf

It is # 46.

Here is the problem as well:

In Fig. 4-44, a ball is thrown up onto a roof, landing 4.00 s later at height h=20.0m above the release level. The ball’s path just before landing is angled at θ = 60.0° with the roof. (a) Find the horizontal distance d it travels. (See the hint to Problem 41.) What are the (b) magnitude and (c) angle (relative to the horizontal) of the ball’s initial velocity?

Given/Known:

t=4.00s

h=20.0m

θ=60.0°

Yo=0

Y=20.0m

ΔY=h

## Homework Equations

I used these:

Voy=(Y-Yo + 0.5gt²)/t

Vo=Voy/(sin θ)

Vox=Vo (cos θ)

Δx=(Vo cos θ) t

magnitude= √[(Vox)²+(Voy)²]

θ=arctan (Y/X)

## The Attempt at a Solution

Solved for Voy, first:

Voy= [20 m + (0.5)(9.8 m/s²)(4 s)²]/ 4 s

=24.6 m/s

then, Vo:

Vo=(24.6 m/s) / (sin 60°)=28.4 m/s

Vox=(28.4 m/s) (cos 60°)= 14.2 m/s

Want:

a) Δx = (28.4 m/s)(cos 60°) (4 s)

= 56.8 m

b) magnitude (V)= √[(14.2 m/s)²+(24.6 m/s)²]= 28.4 m/s

c) θ= (tan ^-1)[(24.6 m/s)/(14.2 m/s)] = 60°

I'm worried my answers seem wrong. Any help would be greatly appreciated.