# Projectile Motion Using Vectors

1. Sep 18, 2011

### VKK

1. The problem statement, all variables and given/known data

A ball is shot from the ground into the air. At a height of 8.7 m, its velocity is = 7.1 + 6.1 m/s, with horizontal and upward. (a) To what maximum height does the ball rise? (b) What total horizontal distance does the ball travel? What are the (c) magnitude and (d) angle (below the horizontal; give as negative) of the ball's velocity just before it hits the ground?

2. Relevant equations
The Kinematics equations

3. The attempt at a solution
im really not sure how to start this problem... do i take the square root of 7.1^2 + 6.1^2 and use that as V0x and Vx, then solve for T? This is one of the last questions i need on wileyplus to get over a 9/10 on homework...

Ive looked at the practice exam for wednesday and its sooo muche easier than these problems. might be freaking out for no reason??

Thanks.

2. Sep 18, 2011

### Delphi51

This is not very clear. Does it mean the velocity is 13.2, or does it mean the horizontal velocity is 7.1 and the vertical velocity 6.1? Check to see if you have typed it in correctly.

Assuming Vx = 7.1 and Vy = 6.1, you could use these as the initial velocities in the equations for horizontal and vertical motion to find anything you like. No, you would not combine 7.1 and 6.1 with the Pythagorean theorem - you need the horizontal and vertical parts separately to put in the equations.

3. Sep 18, 2011

### VKK

the problem didnt copy right..

7.1 i + 6.1 j so yes, horizontal is first, vertical is second.

4. Sep 18, 2011

### Delphi51

Excellent. Do you know the equation for the horizontal motion (constant speed) and the distance and speed equations for the vertical motion (accelerated)? It is a good idea to write down all three, put in all the numbers you know and then try to solve one of the equations to find out something you didn't already know. Part (a) asks about maximum height, where you know the vertical velocity.

5. Sep 18, 2011

### VKK

im just confused for the vector notation of direction. i know how to take the equations and solve for what i need. the velocity given in vector noation is throwing me off.

6. Sep 18, 2011

### Delphi51

Just a way of giving you the horizontal and vertical velocity.
Solve it just the way you did in grade 11.