# Homework Help: Vector Kinematics

1. Sep 21, 2008

### homeworkboy

A skier is accelerating down a 30.0 degree hill at 1.80 m/s2.

What is the vertical component of her acceleration?

How long will it take her to reach the bottom of the hill, assuming she starts from rest and accelerates uniformly, if the elevation change is 375 m

Last edited: Sep 21, 2008
2. Sep 21, 2008

### Mattowander

What effort have you made to solve this problem?

3. Sep 21, 2008

### homeworkboy

I dont even understand how it should be approached

4. Sep 21, 2008

### naele

Draw a picture of what's going on. X and y axes and a vector from the origin going 30 degrees from the horizontal downward. Then break it into its component vectors. The one pointing down is your vertical acceleration

5. Sep 21, 2008

### Mattowander

To find the vertical or horizontal component of any vector is simple trig. To break a vector into components, you usually use the formulas

Vy = VSin(a)
Vx = VCos(a)

Where a is the angle from the horizontal and V is any given vector.

Once you have the vertical component of acceleration, you're ready to solve using kinematics.

You have the acceleration, the height of the hill, and the initial velocity is 0. Which equation could you use to solve for time?

6. Sep 21, 2008

### homeworkboy

Oh ok...i thought that trigonometry of vectors only applies when we are dealing with velocity..sorry..thanks i got the sum...i then used the second eq of motion....
X=Vot + 1/2at2

7. Sep 21, 2008

### MuckThatGuy

Nope... Force vectors are the most common in your course. You can use vectors to describe velocity, but be sure not to mix them into your free-body diagrams.

8. Sep 21, 2008

### homeworkboy

i got another one

A baseball is hit with a speed of 27.0 m/s at an angle of 49.0 degrees. It lands on the flat roof of a 14.0 m tall nearby building.If the ball was hit when it was 1.4 m above the
ground, what horizontal distance does it travel before it lands on the building?

9. Sep 21, 2008

### homeworkboy

i found the time using t = 2Voy/g which came out to be 4.2 seconds....and then wat do i do??