# Homework Help: Projectile motion

1. Feb 11, 2008

### iamkristing

1.a stone is projected at a cliff of height h with an initial speed of 46.0 m/s directed 60.0° above the horizontal. The stone strikes the cliff, 5.10 s after launching.

(a) Find the height, h, of the cliff.

(b) Find the speed of the stone just before impact at A.

(c) Find the maximum height H reached above the ground.

2. Relevant equations

3. The attempt at a solution

i was able to answer a and b. c was giving me trouble. i divided the horizontal and vertical velocities and tried to solve from there but could not come up with an answer

2. Feb 11, 2008

### G01

You know the height of the cliff, correct?

Now, can you find the maximum height the ball reaches above it's starting point (top of the cliff)? If you can, you should be able to answer c.

Try drawing a diagram if you do not see how this helps you obtain the answer.

3. Feb 12, 2008

### iamkristing

Sorry I should clarify the question.

The stone is launched from 0 m and lands on a cliff with a height of 75.5 m. I'm looking for the maximum height of the stone...

4. Feb 12, 2008

### physixguru

use ...
max ht=[vo^2sin^2 theta]/2g

in plave of vo put the 46 m/s you have.

5. Feb 12, 2008

### G01

Ahh ok that makes it clearer. I must have read the problem incorrectly. I read "projected off the cliff, instead of "at the cliff."

HINT: To find the maximum height work with the y direction information.

What is the speed in the y direction at the highest point?

What is the initial speed in the y direction?

What about the acceleration in the y direction?

Can you use this information to find the change in position, i.e. the height of the highest point?