# Homework Help: Projectile Motion (I think)

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1. Nov 11, 2014

### Gingerclaire_

Dave Johnson, the bronze medallist at the 1992 Olympic decathalon in Barcelona, leaves the ground at the high jump with vertical velocity component 6 m/s. How far does his center of mass move up as he makes the jump?

2. Nov 11, 2014

### nasu

You only need to look at the vertical component of the motion.

3. Nov 11, 2014

### BvU

Hello Ginger, welcome to PF :)

Nice exercise. Somewhere along the line the template fell away. It's use is mandatory for good reasons. (Read the guidelines).

In this case you posted only the problem statement. What equations, tools, stuff have you available to tackle it ? Place them under 2). And what have you tried and what came out ? Put that under 3). Help is on the way...

1. The problem statement, all variables and given/known data
2. Relevant equations
3. The attempt at a solution​

4. Nov 11, 2014

### Gingerclaire_

5. Nov 11, 2014

### BvU

Anything in your recent past (lectures, for instance) or in the preceding pages of your textbook that might help ?

6. Nov 11, 2014

### Gingerclaire_

We have been looking at Work, Energy & Power or Energy Conservation but I can't see anything relevant.

7. Nov 11, 2014

### SteamKing

Staff Emeritus
How about gravity? Anything to do with dropping stuff off a cliff or out a window?

8. Nov 11, 2014

### Gingerclaire_

Do you do a kinetic energy equation? Sorry I think I'm making it more difficult for myself here

9. Nov 11, 2014

### SteamKing

Staff Emeritus
A guy jumps off the ground. What forces are working on him so he doesn't go into orbit around the earth?

If you throw a ball up in the air, why does it come back down to the ground?

10. Nov 11, 2014

### Gingerclaire_

So there is a force acting upward - work. Am I right?

11. Nov 11, 2014

### SteamKing

Staff Emeritus
Work is not a force. Once the jumper leaves the ground, there is only one thing affecting his body. What is it? If you pick up a book and drop it on the floor, why does the book fall?

12. Nov 11, 2014

### Gingerclaire_

Oh it is gravity then! So you work out time (t=0.612) and then find displacement (s=3.67)

13. Nov 11, 2014

### SteamKing

Staff Emeritus
As always, show the units with you calculations.