# Homework Help: Projectile; centre on gravity

1. Sep 1, 2011

### bionut

1. The problem statement, all variables and given/known data
A jumper takes off with a velocity of 5 ms at an angle of 20 degrees to the horizontal.
How high does he raise his center of gravity?

2. Relevant equations

3. The attempt at a solution
I know that Vh= 5scos20 = 1.7 m/s and Vv=5Csin20=4.70 m/s

0=5sin20 + 2 X-9.81d
19.62d=1.7
d=1.7/19.62
d=0.087m, but its incorrect. Am I misssing something? The only Thing I can think of is beacuse its his centre of gravity that I should treat it as a vertical launnched projectile?

Last edited: Sep 1, 2011
2. Sep 1, 2011

### PeterO

Nothing wrong with your calculation. Since they are asking how high, could this be the high-jump and the angle is actually 20 degrees to the vertical?

3. Sep 1, 2011

### bionut

thanks for your help, thats what i was thinking would it then mean that the Vv is 5Cos20 instead of 5Sin20? Is that what you are suggesting?, also the answer is 0.14m...

4. Sep 1, 2011

### bionut

Can anyone else help... I still cant get 0.14m???

:-(